CN109792055B - Metal foil film current collector combined with humic acid and battery and super capacitor containing metal foil film current collector - Google Patents

Abstract

A humic acid bound metal foil current collector in a battery or supercapacitor, the current collector comprising: (a) A thin metal foil having two opposing but parallel major surfaces; and (b) a thin film of Humic Acid (HA) or a mixture of HA and graphene, the thin film having hexagonal carbon planes, wherein HA or both HA and graphene are chemically bound to at least one of the two major surfaces; wherein the thin film has a thickness of from 10nm to 10 μm, an oxygen content of from 0.01% to 10% by weight, an interplanar spacing between hexagonal carbon planes of from 0.335 to 0.50nm, from 1.3 to 2.2g/cm ³ All hexagonal carbon planes are oriented substantially parallel to each other and to the major surface, exhibiting a thermal conductivity greater than 500W/mK, and/or an electrical conductivity greater than 1,500s/cm, when measured alone in the absence of the metal foil.

Description

Metal foil film current collector combined with humic acid and battery and super capacitor containing metal foil film current collector

Cross Reference to Related Applications

This application claims priority to U.S. patent application Ser. Nos. 15/243589 and 15/243606, each filed 2016, 8, 22, 2016, and which are hereby incorporated by reference.

Technical Field

The invention provides a current collector for a lithium battery or a super capacitor. The current collector is a metal foil incorporating a thin film of highly oriented humic acid or a humic acid derived highly conductive graphite film.

Background

The present application relates to a current collector that works with the anode electrode (anode active material layer) or cathode electrode (cathode active material layer) of lithium cells (e.g., lithium ion cells, lithium-metal cells, or lithium ion capacitors), supercapacitors, non-lithium cells (e.g., zinc-air cells, nickel metal hydride cells, sodium ion cells, and magnesium ion cells), and other electrochemical energy storage cells. The present application is not a part of the anode active material layer or the cathode active material layer itself.

Lithium-metal cells include conventional lithium-metal rechargeable cells (e.g., using lithium foil as the anode and MnO ₂ Particles as cathode active material), lithium-air cells (Li-air), lithium-sulfur cells (Li-S), and emerging lithium-graphene cells (Li-graphene, using graphene sheets as cathode active material), lithium-carbon nanotube cells (Li-CNT, using CNT as cathode), and lithium-nanocarbon cells (Li-C, using nanocarbon fibers or other nanocarbon materials as cathode). The anode and/or cathode active material layers may contain some lithium, or may be prelithiated prior to cell assembly or immediately thereafter.

Rechargeable lithium ion (Li-ion), lithium metal, lithium-sulfur, and Li metal-air batteries are known for use in Electric Vehicles (EV), hybrid Electric Vehicles (HEV), and portable electric vehicles (HEV)Promising power sources for sub-devices, such as portable computers and mobile phones. With any other metal or metal-intercalating compound (other than Li) as the anode active material _4.4 Si, which has a specific capacity of 4,200mah/g), lithium as a metal element has the highest lithium storage capacity (3,861mah/g). Thus, in general, li metal batteries (with lithium metal anodes) have significantly higher energy densities than conventional lithium ion batteries (with graphite anodes).

Historically, rechargeable lithium metal batteries have used non-lithiated compounds such as TiS that have a relatively high specific capacity ₂ 、MoS ₂ 、MnO ₂ 、CoO ₂ And V ₂ O ₅ Produced as cathode active materials, which are coupled to lithium metal anodes. When the battery is discharged, lithium ions are transferred from the lithium metal anode to the cathode through the electrolyte, and the cathode becomes lithiated. Unfortunately, upon repeated charging and discharging, lithium metal causes dendrite formation at the anode, which eventually causes internal short circuits, thermal runaway, and explosion. Due to a series of accidents related to this problem, the production of these types of secondary batteries was stopped in the early nineties of the twentieth century, and lithium ion batteries were used instead. Even now, for EV, HEV and microelectronic device applications, cycling stability and safety issues remain major factors that hinder further commercialization of Li metal batteries (e.g., lithium-sulfur and lithium-transition metal oxide cells).

The development of lithium ion secondary batteries in which carbonaceous materials (e.g., natural graphite particles) replace pure lithium metal sheets or films as anode active materials has been promoted by the aforementioned concerns about the safety of early lithium metal secondary batteries. The carbonaceous material absorbs lithium (e.g., by intercalation of lithium ions or atoms between graphene planes) and desorbs lithium ions during the recharge and discharge phases, respectively, of the lithium ion battery operation. The carbonaceous material may mainly comprise graphite that may be intercalated with lithium, and the resulting graphite intercalation compound may be represented as Li _x C ₆ Wherein x is typically less than 1 (where the graphite specific capacity is<372mAh/g)。

Although lithium ion (Li-ion) batteries are a promising energy storage device for electrically driven vehicles, state-of-the-art Li-ion batteries have not yet achieved cost, safety, and performance goals (such as high specific energy, high energy density, good cycle stability, and long cycle life). Li ion cells typically use lithium transition metal oxides or phosphates as Li deintercalation/re-intercalation at high potentials relative to a carbon negative electrode (anode) ⁺ Positive electrode (cathode). The specific capacity of cathode active materials based on lithium transition metal oxides or phosphates is typically in the range of 140-170 mAh/g. Thus, the specific energy (gravimetric energy density) of commercially available Li ion cells, characterized by graphite anodes and cathodes based on lithium transition metal oxides or phosphates, is typically in the range of 120-220Wh/kg, most typically 150-200 Wh/kg. Corresponding typical energy densities (volumetric energy densities) range from 400Wh/L to 550Wh/L. Under the condition of high charge-discharge rate, the energy density is even lower. These specific energy values are two to three times lower than would be required if battery-powered electric vehicles were widely accepted.

A typical battery cell consists of: the present invention relates to a battery pack including (a) an anode current collector, (b) an anode electrode (also referred to as an anode active material layer, typically including an anode active material, a conductive filler, and a binder resin component) bonded to the anode current collector with a binder resin, (c) an electrolyte/separator, (d) a cathode electrode (also referred to as a cathode active material layer, typically including a cathode active material, a conductive filler, and a binder resin), (e) a cathode current collector bonded to the cathode electrode with a binder resin, (f) a metal tab connected to an external wire, and (g) a case wrapped around all other components except for these tabs.

The current collectors (typically aluminum foil (at the cathode) and copper foil (at the anode)) make up about 15-20% by weight and 10-15% by cost of the lithium ion battery. Therefore, thinner, lighter foils would be preferred. However, there are several major problems associated with current state of the art current collectors: (a) Thinner foils tend to be more expensive and more difficult to work with due to the ease of wrinkling and tearing; (b) The current collector must be electrochemically stable with respect to the components of the electrode within the operating potential window of the electrode. Indeed, the continuous corrosion of the current collector, mainly caused by the electrolyte, may lead to a gradual increase in the internal resistance of the battery, which leads to a continuous loss of apparent capacity or poor cycle life; (c) Oxidation of the metallic current collector is a strongly exothermic reaction that may contribute significantly to thermal runaway of the lithium battery.

Therefore, the current collector is critical to the cost, weight, safety, and performance of the battery. Instead of metals, graphene or graphene coated solid metals or plastics have been considered as potential current collector materials, as summarized in the references listed below:

li Wang, xiangming He, jianjun Li, jian Gao, mou Fang, guangyu tie, jianlong Wang, shoushan Fan, "Graphene-coated plastic film as current collector for lithium/sulfur batteries" and j.power Source [ journal of power supply ],239 (2013) 623-627.

(2.s.j.) richard prabakrar, yun-Hwa Hwang, eun Gyoung Bae, dong Kyu Lee, myongho pyro, "Graphene oxide as a corrosion inhibitor for the aluminum current collector in lithium ion batteries," Carbon, 52 (2013) 128-136.

Yang Li et al, chinese patent publication No. CN 104600320A (5/6/2015).

Zhaoping Liu et al, (Ningbo Institute of Materials and Energy, china Ningbo Materials & Energy Institute), WO 2012/151880 A1 (11/15/2012).

5.Gwon, H; kim, H-S; lee, KE; seo, D-H; park, YC; lee, Y-S; ahn, BT; kang, K; "Flexible Energy storage devices based on graphene paper" Energy and Environmental Science 4 (2011) 1277-1283.

Ramesh c. Bhardwaj and Richard m. Mank, "Graphene current collectors in batteries for portable electronic devices" US 20130095389 A1, year 2013, month 4 and day 18.

Currently, there are three different forms of graphene current collectors: graphene coated substrates [ references 1-4], free standing graphene paper [ reference 5], and single layer graphene films produced by transition metal (Ni, cu) catalyzed Chemical Vapor Deposition (CVD) followed by metal etching [ reference 6].

In the preparation of graphene coated substrates, small isolated sheets or platelets of Graphene Oxide (GO) or Reduced Graphene Oxide (RGO) are spray deposited onto a solid substrate (e.g., plastic film or Al foil). In the graphene layer, the structural units are separate graphene sheets/platelets (typically 0.5-5 μm in length/width and 0.34-30nm in thickness) that are typically bound by a binder resin such as PVDF [ references 1,3, and 4]. While individual graphene sheets/platelets may have relatively high conductivity (within the 0.5-5 μm limit), the resulting graphene-binder resin composite layer is relatively poor in conductivity (typically <100S/cm and more typically < 10S/cm). Further, another purpose of using the binder resin is to bond the graphene-adhesive composite layer to a substrate (e.g., cu foil); this means that there is a binder resin (adhesive) layer between the Cu foil and the graphene-binder composite layer. Unfortunately, this adhesive resin layer is electrically insulating and the resulting detrimental effects appear to have been completely overlooked by current workers.

Although Prabakan et al [ reference 2]]There does not appear to be the use of a binder resin to form an aluminum foil coated with discrete graphene oxide sheets, but this graphene oxide coated Al foil has its own problems. As is well known in the art, aluminum oxide (Al) ₂ O ₃ ) Easily formed on the surface of the aluminum foil and cleaning with acetone or alcohol does not remove this aluminum oxide or alumina passivation layer. This aluminum oxide layer is not only electrically and thermally insulating, but is virtually intolerant to certain types of electrolytes. For example, the most commonly used lithium ion battery electrolytes areLiPF dissolved in organic solvent ₆ . Trace amount of H in the electrolyte ₂ O may trigger a series of chemical reactions involving the formation of HF (a highly corrosive acid) which readily decomposes the aluminum oxide layer and continues to corrode the Al foil and consume electrolyte. Capacity fade typically becomes more pronounced after 200-300 charge-discharge cycles.

Free standing graphene paper is typically prepared by vacuum assisted filtration of GO or RGO platelets/platelets suspended in water. In stand-alone paper, the structural units are separate graphene sheets/platelets that are loosely stacked together. Again, while individual graphene sheets/platelets may have relatively high conductivity (within the 0.5-5 μm limit), the resulting graphene paper has very low conductivity; for example, 8,000S/m or 80S/cm [ reference 5]]Electrical conductivity (8x 10) of Cu foil ⁵ S/cm) by 4 orders of magnitude.

There are several major problems associated with the most commonly used method of producing graphene (i.e. the chemical oxidation/intercalation method):

(1) The process requires the use of large amounts of several undesirable chemicals, such as sulfuric acid, nitric acid, and potassium permanganate or/and sodium chlorate.

(2) Thermal expansion requires high temperatures (typically 800-1,050 ℃) and is therefore a highly energy intensive process.

(3) The process requires very cumbersome washing and purification steps. For example, typically 2.5kg of water is used to wash and recover 1 gram of GIC, producing large amounts of waste water that needs to be properly treated.

(4) The resulting product is Graphene Oxide (GO) platelets, which must undergo further chemical reduction treatment to reduce the oxygen content. Typically, even after reduction, the conductivity of GO platelets is much lower than that of pristine graphene. In addition, reduction procedures often involve the use of toxic chemicals, such as hydrazine.

(5) Further, the amount of intercalation solution that remains on the flakes after draining may range from 20 to 150 parts by weight solution per 100 parts by weight graphite flakes (pph), and more typically about 50 to 120pph. During the high temperature expansion process, the residual intercalated species retained by the flakes decompose to produce a variety of speciesUndesirable sulfur-and nitrogen-containing compounds of the class (e.g. NO) _x And SO _x ). Effluent requires expensive remediation procedures in order not to have adverse environmental effects.

A catalyzed CVD process for graphene production involves introducing a hydrocarbon gas into a vacuum chamber at a temperature of 500-800 ℃. Under these severe conditions, the hydrocarbon gas is decomposed, wherein the decomposition reaction is catalyzed by a transition metal substrate (Ni or Cu). The Cu/Ni substrate is then chemically etched away using strong acids, which is not an environmentally friendly procedure. The overall process is slow, tedious, and energy consuming, and the resulting graphene is typically a single layer graphene or few layers of graphene (up to 5 layers, as the underlying Cu/Ni layer loses its effectiveness as a catalyst).

Bhardwaj et al [ reference 6] suggested stacking multiple CVD-graphene films to a thickness of 1 μm or several μm; however, this would require hundreds or thousands of films stacked together (each film typically 0.34nm to 2nm thick). Although Bhardwaj et al claim that "graphene can reduce manufacturing costs and/or increase energy density of battery cells," no experimental data is presented to support their claim. In contrast to this claim, CVD graphene is a notoriously expensive process, and even a single layer of CVD graphene film will be significantly more expensive than a Cu or Al foil, assuming the same area (e.g., the same 5cm x 5 cm). Stacks of hundreds or thousands of single or few layers of graphene films as suggested by Bhardwaj et al would mean hundreds or thousands of times more expensive than Cu foil current collectors. This cost will be excessively high. Further, the high contact resistance between hundreds of CVD graphene films in the stack and the relatively low electrical conductivity of the CVD graphene will result in a high total internal resistance, making any potential benefit of using thinner films (1 μm graphene stack relative to 10 μm Cu foil) to reduce the total cell weight and volume ineffective. It appears that the patent application by Bhardwaj et al [ reference 6] (without any data) is nothing more than a conceptual document.

The above discussion has clearly shown that all three forms of graphene enhanced or graphene-based current collectors do not meet the performance and cost requirements for use in batteries or supercapacitors. There is a strong demand for different types of materials for use as current collectors.

The present invention relates to a new class of materials, referred to herein as highly oriented Humic Acid (HA) films (alone or in combination with graphene), which are chemically bonded to the surface of metal foils. Graphene as used herein includes pristine graphene, oxidized graphene, fluorinated graphene, nitrogenated graphene, hydrogenated graphene, boron-doped graphene, any other type of doped graphene, and other types of chemically functionalized graphene. Quite unexpectedly and significantly, such a film of highly oriented HA or HA/graphene mixture can be thermally converted into a highly conductive graphite film.

Humic Acid (HA) is an organic substance commonly found in soil and can be extracted from soil using a base such as KOH. HA can also be extracted in high yield from a class of coals known as leonardite, which is a highly oxidized version of lignite. HA extracted from leonardite contains many oxygen-containing groups (e.g., carboxyl groups) located at the center of graphene-like molecules (SP of hexagonal carbon structure) ² Core) around the edge. This material is somewhat similar to Graphene Oxide (GO) produced by oxidizing natural graphite with strong acids. HA HAs a typical oxygen content of 5 to 42% by weight (the other main elements are carbon and hydrogen). After chemical or thermal reduction, HA HAs an oxygen content of 0.01% to 5% by weight. For the purposes defined in the claims in this application, humic Acid (HA) refers to the entire oxygen content range from 0.01% to 42% by weight. Reduced Humic Acid (RHA) is a special type of HA with an oxygen content of 0.01% to 5% by weight.

It has surprisingly been found that humic acid, when brought into intimate contact with the surface of the metal foil, can chemically bind to the metal foil. It was further surprising to find that, when properly aligned and packed together, humic acid molecules can be chemically linked to each other to obtain longer and wider humic acid sheets. These humic acid molecules can also be chemically linked or bound to the graphene sheets (if present and properly arranged and stacked). The resulting thin metal foil incorporating the humic acid or graphite film is electrolyte-compatible, non-reactive, corrosion resistant, low in contact resistance, thermally and electrically conductive, ultra-thin, and lightweight, enabling the battery or capacitor to provide higher output voltages, higher energy densities, high rate capability, and much longer cycle life.

Disclosure of Invention

The present invention provides a metal foil current collector incorporating highly oriented humic acid for use in a battery or supercapacitor. The invention also provides a current collector consisting of a metal foil and a humic acid-derived highly conductive graphite film bonded to one or both major surfaces of the metal foil. The invention also provides methods of producing these current collectors.

The current collector of the present invention comprises: (a) A thin metal foil having a thickness of from 1 to 30 μm (preferably from 4 to 12 μm) and two opposing but substantially parallel major surfaces; and (b) at least one film of highly oriented Humic Acid (HA) or a mixture of HA and graphene sheets (or a highly conductive graphite film derived from such a film) chemically bonded to at least one of the two opposite major surfaces of the metal foil. The thin film of HA or HA/graphene mixture or derived graphite film HAs a thickness of from 10nm to 10 μm, an oxygen content of from 0.01 to 10% by weight, from 1.3 to 2.2g/cm when measured alone without the thin metal foil ³ A hexagonal carbon plane oriented substantially parallel to each other and to the major surface, an interplanar spacing between the hexagonal carbon planes of 0.335 to 0.50nm, greater than 250W/mK (more typically>500W/mK), and greater than 800S/cm (more typically>1,500s/cm).

Preferably, each of the two opposite main surfaces is chemically bonded to a thin film of such humic acid or HA/graphene mixture or to a graphite film derived from this thin film produced by heat treatment. It is also preferred that one or both of the films of HA or both HA and graphene (or derivatized graphite film) be chemically bonded to one or both opposing major surfaces of the metal foil without the use of a binder or adhesive. If a binder is used, the binder is a conductive material selected from the group consisting of intrinsically conductive polymers, pitch, amorphous carbon, or carbonized resins (polymeric carbons). Preferably, the thin metal foil has a thickness of from 4 to 12 μm. Also preferably, the thin film or graphite film of humic acid or HA/graphene mixture HAs a thickness of from 20nm to 2 μm.

For the current collector, preferably, the metal foil is selected from Cu, ti, ni, stainless steel, al foil, or a combination thereof. Preferably, the major surface does not contain a passivating metal oxide layer thereon (e.g., no aluminum oxide, al, on the surface of the Al foil) ₂ O ₃ )。

Preferably, the thin film of HA or HA/graphene mixture or the graphite film derived therefrom HAs an oxygen content of from 1 to 5% by weight. Further preferably, the thin film or graphitic film derived therefrom has an oxygen content of less than 1%, an interplanar spacing of less than 0.345nm, and an electrical conductivity of no less than 3,000s/cm. More preferably, the thin film or graphitic film derived therefrom has an oxygen content less than 0.1%, an interplane spacing less than 0.337nm, and an electrical conductivity no less than 5,000s/cm. Still more preferably, the thin film or a graphite film derived therefrom has an oxygen content of no greater than 0.05%, an interplanar spacing of less than 0.336nm, a splay to mosaic value of no greater than 0.7, and an electrical conductivity of no less than 8,000s/cm. Even more preferably, the thin film or a graphite film derived therefrom has an interplanar spacing of less than 0.336nm, a mosaic spread value of no greater than 0.4, and an electrical conductivity of greater than 10,000s/cm.

More preferably, the thin film of HA or HA/graphene mixture or graphitic film derived therefrom exhibits an interplanar spacing of less than 0.337nm and a mosaic spread value of less than 1.0. Most preferably, the thin film or graphite film derived therefrom exhibits a degree of graphitization of not less than 80% and/or a mosaic spread value of not more than 0.4.

In certain embodiments, the film of HA or HA/graphene mixture is obtained by: depositing a suspension of HA or a mixture of HA and graphene sheets onto the at least one major surface under the influence of an orientation-controlling stress to form a layer of HA or a mixture of HA and graphene sheets, and then heat-treating the layer at a heat-treatment temperature of from 80 ℃ to 1,500 ℃. More preferably, the heat treatment temperature is from 80 ℃ to 500 ℃ and still more preferably from 80 ℃ to 200 ℃.

The highly oriented thin film of HA or HA/graphene or graphite film derived therefrom bonded to the underlying current collector typically contains mutually parallel chemically bonded humic acid molecules or chemically combined humic acid and graphene planes as shown in fig. 3 (C). Preferably, the film is a continuous length film having a length of not less than 5cm and a width of not less than 1cm, and this film is made by a roll-to-roll (roll) process.

Preferably, the thin film of HA or HA/graphene mixture or graphite film derived therefrom HAs a physical density of greater than 1.6g/cm3, and/or a tensile strength of greater than 30MPa, when measured alone (as a free standing layer in the absence of metal foil). More preferably, the film or graphite film derived therefrom has a physical density greater than 1.8g/cm3, and/or a tensile strength greater than 50MPa, when measured alone. Most preferably, the thin film or graphite film derived therefrom has greater than 2.0g/cm when measured alone ³ And/or a tensile strength of greater than 80 MPa.

The invention also provides a rechargeable lithium or lithium ion battery comprising the current collector of the invention as an anode current collector and/or a cathode current collector. The rechargeable lithium battery may be a lithium-sulfur cell, a lithium-selenium cell, a lithium sulfur/selenium cell, a lithium-air cell, a lithium-graphene cell, or a lithium-carbon cell.

The invention also provides a capacitor comprising the current collector of the invention as an anode current collector or a cathode current collector, wherein the capacitor is a symmetric supercapacitor, an asymmetric supercapacitor cell, a hybrid supercapacitor-battery cell, or a lithium ion capacitor cell.

The invention also provides a method for producing a metal foil current collector incorporating a highly oriented humic acid film for use in a battery or supercapacitor. The method comprises the following steps:

(a) Preparing a dispersion of Humic Acid (HA) or chemically functionalized humic acid (CHA) flakes dispersed in a liquid medium, wherein said HA flakes contain an oxygen content above 5% by weight or said CHA flakes contain a non-carbon element content above 5% by weight;

(b) Dispensing and depositing said HA or CHA dispersion onto at least one major surface of a metal foil to form a wet layer of HA or CHA on said surface, wherein said dispensing and depositing procedure comprises subjecting said dispersion to orientation-inducing stress;

(c) Partially or completely removing the liquid medium from the wet layer of HA or CHA to form a composite having hexagonal carbon planes and an interplanar spacing d between 0.4nm and 1.3nm as determined by X-ray diffraction ₀₀₂ The dried HA or CHA layer of (a); and

(d) Heat treating the dried HA or CHA layer at a first heat treatment temperature above 80 ℃ for a sufficient period of time to produce the metal foil current collector incorporating the highly oriented humic acid film, wherein the humic acid film contains interconnected, merged, or thermally reduced HA or CHA sheets that are substantially parallel to each other and chemically bonded to and parallel to the major surface, and the humic acid film HAs no less than 1.3g/cm ³ A thermal conductivity of at least 250W/mK, and/or an electrical conductivity of not less than 500S/cm. The method may further comprise the step of compressing the humic acid film of the combined or reduced HA or CHA after said step (d).

The method may comprise the further step (e): further heat treating the humic acid film bound metal foil at a second heat treatment temperature higher than the first heat treatment temperature for a sufficient period of time to produce a graphite film bound metal foil current collector, wherein the graphite film has an inter-planar spacing d less than 0.4nm ₀₀₂ And an oxygen content or non-carbon element content of less than 5% by weight; and (f): compressing the graphite film to produce a graphite film having a thickness of not less than 1.3g/cm ³ A thermal conductivity of at least 500W/mK, and/or an electrical conductivity of not less than 1,000s/cm. The highly conductive graphite film preferably has a thickness of from 5nm to 20 μm, but more preferably from 10nm to 2 μm.

The HA or CHA dispersion may further contain graphene sheets or molecules dispersed thereinAnd a ratio of HA to graphene or CHA to graphene is from 1/100 to 100/1, wherein the graphene is selected from pristine graphene, graphene oxide, reduced graphene oxide, fluorinated graphene, brominated graphene, iodinated graphene, boron doped graphene, nitrogen doped graphene, chemically functionalized graphene, or a combination thereof. The method may comprise the further step (e): further heat treating the combined or reduced humic acid film of HA or CHA at a second heat treatment temperature higher than the first heat treatment temperature for a sufficient period of time to produce a film having an inter-planar spacing d of less than 0.4nm ₀₀₂ And less than 5% by weight of an oxygen content or a non-carbon elemental content graphite film; and step (f): compressing the graphite film to produce a graphite film having a thickness of not less than 1.6g/cm ³ A thermal conductivity of at least 700W/mK, and/or an electrical conductivity of not less than 1,500s/cm.

In certain embodiments, the HA or CHA sheet is in an amount sufficient to form a liquid crystal phase in the liquid medium. Preferably, the dispersion comprises a first volume fraction of HA or CHA dispersed in said liquid medium, said first volume fraction exceeding the critical volume fraction (V) for the formation of a liquid crystal phase _c ) And the dispersion is concentrated to achieve a second volume fraction of HA or CHA greater than the first volume fraction to improve HA or CHA flake orientation. Preferably, the first integral number corresponds to a weight fraction of HA or CHA in the dispersion of from 0.05% to 3.0% by weight. Prior to said step (b), the dispersion may be concentrated to contain more than 3.0% but less than 15% by weight of HA or CHA dispersed in the liquid medium.

In some embodiments, the dispersion further comprises a polymer dissolved in said liquid medium or attached to HA or CHA.

The CHA may contain a chemical functional group selected from: polymer, SO ₃ H、COOH、NH ₂ OH, R 'CHOH, CHO, CN, COCl, halide, COSH, SH, COOR', SR ', siR' ₃ 、Si(--OR'--) _y R' _3-y 、Si(--O--SiR' ₂ --)OR'、R"、Li、AlR' ₂ 、Hg--X、TlZ ₂ And Mg- -X; whereinY is an integer equal to or less than 3, R' is hydrogen, alkyl, aryl, cycloalkyl, or aralkyl, cycloaryl, or poly (alkylether), R "is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl, or cycloaryl, X is halide, and Z is carboxylate or trifluoroacetate, or a combination thereof.

The graphene sheets (if present) may contain chemically functionalized graphene containing chemical functional groups selected from: polymer, SO ₃ H、COOH、NH ₂ OH, R 'CHOH, CHO, CN, COCl, halide, COSH, SH, COOR', SR ', siR' ₃ 、Si(--OR'--) _y R' _3-y 、Si(--O--SiR' ₂ --)OR'、R"、Li、AlR' ₂ 、Hg--X、TlZ ₂ And Mg- -X; wherein y is an integer equal to or less than 3, R 'is hydrogen, alkyl, aryl, cycloalkyl, or aralkyl, cycloaryl, or poly (alkylether), R' is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl, or cycloaryl, X is halide, and Z is carboxylate or trifluoroacetate, or combinations thereof.

Preferably, the liquid medium consists of water or a mixture of water and alcohol. Alternatively, the liquid medium contains a non-aqueous solvent selected from: polyethylene glycol, ethylene glycol, propylene glycol, alcohols, sugar alcohols, polyglycerols, glycol ethers, amine-based solvents, amide-based solvents, alkylene carbonates, organic acids, or inorganic acids.

The second heat treatment temperature may be higher than 1,500 ℃ for a time sufficient to reduce the inter-planar spacing d ₀₀₂ To a value of less than 0.36nm and to reduce the oxygen content or the non-carbon element content to less than 0.1% by weight. Specifically, the second heat treatment temperature may be from 1,500 ℃ to 3,200 ℃.

The process is preferably a roll-to-roll or reel-to-reel (reel-to-reel) process, wherein step (b) comprises feeding a sheet of the metal foil from a roll to a deposition zone, depositing a layer of HA or CHA dispersion onto at least one major surface of the metal foil to form a wet layer of HA or CHA dispersion thereon, drying the HA or CHA dispersion to form a dried HA or CHA layer deposited on the surface of the metal foil, and collecting the HA or CHA layer deposited metal foil on a collection roll.

In certain embodiments, the first heat treatment temperature comprises a temperature in the range of 100 ℃ to 1,500 ℃ and the highly oriented humic acid film has an oxygen content of less than 2.0%, an inter-planar spacing of less than 0.35nm, no less than 1.6g/cm ³ A thermal conductivity of at least 800W/mK, and/or an electrical conductivity of not less than 2,500S/cm. In other embodiments, the first heat treatment temperature comprises a temperature in the range of 1,500 ℃ to 2,100 ℃ and the highly oriented humic acid film, becoming a highly conductive graphite film, has an oxygen content of less than 1.0%, an interplanar spacing of less than 0.345nm, a thermal conductivity of at least 1,000w/mK, and/or an electrical conductivity of not less than 5,000s/cm.

In some embodiments, the first and/or second heat treatment temperature comprises a temperature greater than 2,100 ℃, and the highly conductive graphite film has an oxygen content of no greater than 0.1%, an inter-graphene spacing of less than 0.340nm, a mosaicism value of no greater than 0.7, a thermal conductivity of at least 1,300w/mK, and/or an electrical conductivity of no less than 8,000s/cm. If the second heat treatment temperature comprises a temperature of not less than 2,500 ℃, the highly conductive graphite film has an inter-graphene spacing of less than 0.336nm, a mosaic spread value of not greater than 0.4, a thermal conductivity of greater than 1,500w/mK, and/or an electrical conductivity of greater than 10,000s/cm. The graphitization degree may be not less than 80% and the mosaic spread value is less than 0.4.

Typically, the HA or CHA flakes have a maximum original length, and the highly oriented humic acid film comprises HA or CHA flakes having a length greater than said maximum original length. This means that some humic acid molecules merge with other HA molecules in an edge-to-edge manner to increase the length or width of the planar molecule or sheet. The heat treatment step (e) causes chemical linking, merging, or chemical bonding of the HA or CHA sheets with other HA or CHA sheets, or with graphene sheets to form a graphitic structure. The highly conductive graphite film is a polycrystalline graphene structure having a preferred crystallographic orientation as determined by the X-ray diffraction method.

The process typically results in the formation of a highly oriented graphite film having a conductivity greater than 5,000S/cmA thermal conductivity of more than 800W/mK, more than 1.9g/cm ³ A tensile strength of greater than 80MPa, and/or an elastic modulus of greater than 60 GPa. Further typically, the highly oriented graphite film has an electrical conductivity greater than 8,000S/cm, a thermal conductivity greater than 1,200W/mK, greater than 2.0g/cm ³ A tensile strength of greater than 100MPa, and/or an elastic modulus of greater than 80 GPa. The highly oriented graphite film has an electrical conductivity greater than 12,000S/cm, a thermal conductivity greater than 1,500W/mK, a thermal conductivity greater than 2.1g/cm using a final heat treatment temperature (first or second heat treatment temperature) greater than 1,500 deg.C ³ A tensile strength of greater than 120MPa, and/or an elastic modulus of greater than 120 GPa.

Drawings

Fig. 1 (a) shows a flow diagram of various prior art processes for producing expanded graphite products (flexible graphite foil and flexible graphite composite) and pyrolytic graphite (bottom part).

Fig. 1 (B) is a process for producing isolated graphene sheets and aggregates of graphene or graphene oxide sheets in the form of graphene paper or thin film.

Fig. 1 (C) is a method for producing isolated graphene sheets and aggregates of graphene or graphene oxide sheets in the form of graphene paper or thin film.

Fig. 2 is an SEM image of a cross-section of a flexible graphite foil showing a number of graphite flakes having an orientation that is not parallel to the plane of the flexible graphite foil surface, and also showing a number of defects, kinked or folded flakes.

Fig. 3 (a) SEM image of HA liquid crystal-derived HOGF, wherein multiple hexagonal carbon planes are seamlessly merged into graphene-like sheets or layers of continuous length that may extend tens of centimeters wide or long (only 50 μm width of 10-cm wide HOGF is shown in this SEM image);

fig. 3 (B) SEM images of cross-sections of conventional graphene paper prepared from discrete reduced graphene oxide sheets/platelets using a papermaking process (e.g., vacuum assisted filtration). The image shows a number of folded or broken (not integrated) discrete graphene sheets having an orientation that is not parallel to the film/paper surface, and having a number of defects or imperfections;

FIG. 3 (C) is a schematic representation of the chemical coalescence of highly oriented molecular films of humic acid to form a highly ordered and conductive graphite film.

FIG. 4 (A) thermal conductivity values for HA/GO derived HOGF, HA derived HOGF, and FG foils plotted as a function of final heat treatment temperature;

FIG. 4 (B) thermal conductivity values for HA/GO derived HOGF, HA derived HOGF, and polyimide derived HOPG, all plotted as a function of final HTT; and is provided with

Fig. 4 (C) conductivity values for HA/GO derived HOGF, HA derived HOGF, and FG foil plotted as a function of final heat treatment temperature.

Fig. 5 (a) graphene interplanar spacing in HA-derived HOGF as measured by X-ray diffraction;

FIG. 5 (B) oxygen content in HA-derived HOGF;

FIG. 5 (C) correlation between inter-graphene spacing and oxygen content; and is

Fig. 5 (D) thermal conductivity values for HA/GO derived HOGF, HA derived HOGF, and FG foil plotted as a function of final heat treatment temperature.

Figure 6 thermal conductivity of HOGF samples plotted as a function of the proportion of GO sheets in the HA/GO suspension.

Fig. 7 (a) tensile strength values for HA/GO derived HOGF, HA derived HOGF, flexible graphite foil, and reduced graphene oxide paper, all plotted as a function of final heat treatment temperature;

fig. 7 (B) tensile moduli of HA/GO derived HOGF, and HA derived HOGF plotted as a function of final heat treatment temperature.

Figure 8 thermal conductivity of three HA-derived highly oriented films; an HA film peeled from a glass surface by heat treatment, one deposited and bonded to a Ti surface at the time of heat treatment, and one deposited and bonded to a Cu foil surface at the time of heat treatment.

FIG. 9 (A) discharge capacity values for three Li-S cells, each as a function of the number of charge/discharge cycles; the first cell HAs a Cu foil bonded to HA and an Al foil bonded to HA as anode and cathode current collectors, respectively; the second cell (prior art cell) had GO/resin coated Cu foil and GO coated Al foil (without pre-etching) as anode and cathode current collectors, respectively; the third cell (prior art cell) had a Cu foil anode current collector and an Al foil cathode current collector.

Fig. 9 (B) Ragone plots for the following three cells: the first cell HAs a Cu foil bonded to HA and an Al foil bonded to HA as anode and cathode current collectors, respectively; the second cell (prior art cell) had GO/resin coated Cu foil and GO coated Al foil (without pre-etching) as anode and cathode current collectors, respectively; the third cell (prior art cell) had a Cu foil anode current collector and an Al foil cathode current collector.

Fig. 10 cell capacity values for the following three magnesium metal cells: the first cell HAs a Cu foil bonded to HA and an Al foil bonded to HA as anode and cathode current collectors, respectively; the second cell (prior art cell) had GO/resin coated Cu foil and GO coated Al foil (without pre-etching) as anode and cathode current collectors, respectively; the third cell (prior art cell) had a Cu foil anode current collector and an Al foil cathode current collector.

Detailed Description

The present invention provides a humic acid-bonded metal foil thin film current collector for use in a battery or supercapacitor (e.g., as schematically shown in fig. 1 (C)). In a preferred embodiment, the current collector comprises: (a) A free-standing, unsupported, thin metal foil (214 in fig. 1 (C)) having a thickness of from 1 to 30 μ ι η and two opposing but substantially parallel major surfaces; and (b) a thin film 212 of Humic Acid (HA) or HA/graphene mixture chemically bonded to at least one of the two opposing major surfaces (without the use of a binder or adhesive). Fig. 1 (C) shows only one major surface of the metal foil 214 bonded to a thin film 212 of HA or HA/graphene mixture. Preferably, however, the opposite major surface is also bonded to a thin film of HA or HA/graphene mixture (not shown in fig. 1 (C)). As an end terminal for electrically connecting the battery/supercapacitor to an external circuit, the metal tabs 218 are typically welded or brazed to the metal foil 214.

As shown in fig. 1 (C), a preferred embodiment of the present invention is a metal foil current collector incorporating HA, where there is no adhesive resin layer or passivating aluminum oxide layer between the film of HA or HA/graphene mixture and the Cu or Al foil. In contrast, as schematically shown in fig. 1 (B), graphene coated metal foil current collectors of the prior art typically and necessarily require an adhesive resin layer between the graphene layer (graphene-resin composite) and the metal foil (e.g., cu foil). Graphene coated Al foils in the prior art [ prabakrar et Al; reference 2] a passivating aluminum oxide (alumina) layer naturally exists between the graphene layer and the Al metal foil. This is due to the well-known fact that: when manufactured and exposed to room air, the aluminum foil always forms a passivating aluminum oxide layer on the Al foil surface. This alumina layer cannot be removed by simple cleaning with acetone or alcohol. As will be elucidated in the following paragraphs, the presence of the binder resin or the aluminum oxide layer (even as thin as only 1 nm) has a great influence on increasing the contact resistance between the graphene layer and the metal foil. Our surprising discovery was completely ignored by all prior art workers, and thus, the prior art graphene-coated metal foils did not meet the performance and cost requirements of lithium battery or supercapacitor current collectors.

The very significant and unexpected advantage of bringing humic acid pieces in direct contact with the main surface of a Cu, ni, steel, or Ti foil lies in the following view: the HA molecules can bond well to these metal foils under the processing conditions of the present invention without the use of external resin binders or adhesives (thus, without significantly increasing the contact resistance). These processing conditions include having the HA (or mixture of HA and graphene) molecules or sheets well aligned on the metal foil surface and then heat treating the two-layer structure at a temperature in the range of 80 ℃ to 1,500 ℃ (more typically and desirably 80 ℃ to 500 ℃, and most typically and desirably 80 ℃ to 200 ℃). Optionally, but not preferably, the heat treatment temperature may be as high as 1,500 ℃ -3,000 ℃ (provided the metal foil can withstand such high temperatures).

In the case of aluminium foil based current collectors, these processing conditions preferably include chemical etching away of the passivated aluminium oxide layer before coating and bonding with HA, followed by heat treatment under comparable temperature conditions as described above. Alternatively, the HA molecule may be prepared in an acidic state, characterized by having a high oxygen content (reflecting high amounts of-OH and-COOH groups) and having less than 5.0 (preferably<3.0 and even more preferably<2.0 ) pH value of the solution. The Al foil may be immersed in a HA solution bath, where the acidic environment naturally removes the passivating Al ₂ O ₃ And (3) a layer. When the Al foil emerges from the bath, the HA molecules or sheets naturally adhere to the clean, etched Al foil surface, effectively preventing exposure of the Al foil surface to open air (thus, there is no passivating Al between the Al foil surface and the HA layer) ₂ O ₃ Layer and no increased contact resistance). This strategy has never been disclosed or suggested before.

In addition to the chemical binding capacity of the inventive HA layer and the chemical etching capacity of the HA solution, the resulting film of HA or HA/graphene mixture in the inventive HA-bound metal foil HAs a thickness of from 10nm to 10 μm, an oxygen content of from 0.1% to 10% by weight, an interplanar spacing of graphene of from 0.335nm to 0.50nm, from 1.3 to 2.2g/cm ³ All HA and graphene sheets (if present) oriented substantially parallel to each other and to the major surfaces, when measured alone in the absence of a thin metallic foil, exhibit a thermal conductivity greater than 500W/mK and/or an electrical conductivity greater than 1,500s/cm. This thin film of HA or HA/graphene is chemically inert and provides a highly effective protective layer against corrosion of the underlying metal foil.

Now, let us examine in detail the magnitude of the total resistance (including the contact resistance) in the three-layer structure as shown in fig. 1 (B). The electrons in the graphene layer 202 (layer 1) must move around in this layer, move through the adhesive resin or passivating aluminum oxide layer 206 (layer 2), and then move in the metal foil layer 204 (layer 3) towards the terminal tab 208. For simplicity, we will only consider the total resistance for electrons moving through the thickness of the graphene layer, the thickness of the adhesive/passivation layer, and the thickness of the metal foil layer. Electron movement in the in-plane direction of both graphene or metal foil is rapid and low resistance; therefore, this resistance is ignored in the calculation of the present invention.

The thickness direction resistance of the conductor sheet/film is given by: r = (1/σ) (t/a), where a = cross-sectional area (length × width) of the conductor, t = thickness of the conductor,

the graphene coated current collector containing the adhesive or the passivated metal oxide layer may be regarded as a three-layer structure having a graphene film, an interfacial adhesive resin layer (or a passivated aluminum oxide layer), and a metal foil layer electrically connected in series (fig. 1 (B)).

The total resistance is the sum of the resistance values of the three layers: r = R ₁ +R ₂ +R ₃ ＝ρ ₁ (t ₁ /A ₁ )+ρ ₂ (t ₂ /A ₂ )+ρ ₃ (t ₃ /A ₃ )＝(1/σ ₁ )(t ₁ /A ₁ )+(1/σ ₂ )(t ₂ /A ₂ )+(1/σ ₃ )(t ₃ /A ₃ ) Where ρ = resistivity, σ = conductivity, t = thickness, and a = area of layer, and approximately, a ₁ ＝A ₂ ＝A ₃ . Scanning electron microscopy revealed that the binder resin or passivated alumina layer was typically 5-100nm thick. Electrical resistivity of most commonly used binder resins (PVDF) and alumina (Al) ₂ O ₃ ) Typically 10 ¹³ -10 ¹⁵ In the ohm-cm range. Suppose A ₁ ＝A ₂ ＝A ₃ ＝1cm ² Thickness direction resistivity ρ of graphene layer ₁ =0.1 ohm-cm, adhesive or alumina layer resistivity ρ ₂ ＝1×10 ¹⁴ Ohm-cm and the metal foil layer resistivity is p ₃ ＝1.7×10 ^-6 Ohm-cm (Cu foil), or rho ₃ ＝2.7×10 ^-6 Ohm-cm (Al foil)). The optimum conditions were also assumed where Cu foil or Al foil thickness =6 μm, graphene layer thickness =1 μm, and adhesive resin layer thickness was only 0.5nm (actually it was from 5nm to 100 nm). The total resistance of the three-layer structure will be 5x10 ⁶ Ohm and bulk conductivity will be as low as 1.4 x10 ^-10 S/cm (see first data line in Table 1 below). If we assume that the adhesive resin layer is 10nm thick, the total resistance of the three-layer structure will be 1 × 10 ⁸ Ohm and overall conductivity will be as low as 7.0 x10 ^{- 12} S/cm (see data line 4 in Table 1 below). Such a 3-layer composite structure would not be a good current collector for a battery or supercapacitor, since high internal resistance would mean low output voltage and high amount of internal heat generation. Similar results were observed for Ni foil, ti foil, and stainless steel foil based current collectors (data rows 7-10 in table 1).

Table 1:

in contrast, if the binder resin or alumina layer is not present (t) ₂ = 0) (as in the case of the current collector of the invention), the total resistance of the Cu foil combined with graphene oxide had 1.0 × 10 ^-5 Ohm value (1.0X 10 with 3-layer structure containing 1- μm adhesive resin layer ⁺⁷ Ohmic phase). See table 2 below. This represents a difference of 12 orders of magnitude (not 12 times) |! 7.0X 10 of corresponding 3-layer structure ^-11 In contrast to S/cm, for the 2-layer structure of the invention, the conductivity would be 7.0X 10 ⁺¹ S/cm. Again, the difference is 12 orders of magnitude. Furthermore, we have found that lithium batteries and supercapacitors featuring the graphene oxide-bonded metal foil current collectors of the present invention always exhibit higher voltage output, higher energy density, higher power density, more stable charge-discharge cycling response, and last longer without capacity fade or corrosion problems compared to prior art graphene-based current collectors.

Table 2:

in the following, descriptions of humic acid and graphene, which are two main components in a thin film coated on a metal foil, are presented.

Bulk natural flake graphite is a 3-D graphite material in which each particle is composed of a plurality of grains (the grains are graphite single crystals or crystallites) having grain boundaries (amorphous or defect regions) that define adjacent graphite single crystals. Each grain is composed of a plurality of graphene planes oriented parallel to each other. The graphene planes in the graphite crystallites are composed of carbon atoms occupying a two-dimensional hexagonal lattice. In a given grain or single crystal, graphene planes are stacked in the crystallographic c-direction (perpendicular to the graphene plane or basal plane) and bound by van der waals forces. While all graphene planes in one grain are parallel to each other, typically the graphene planes in one grain and the graphene planes in an adjacent grain are different in orientation. In other words, the orientation of the different grains in the graphite particles typically differs from one grain to another.

Graphite single crystals (crystallites) are themselves anisotropic, with properties measured in the direction of the basal plane (crystallographic a-or b-axis direction) being significantly different from those measured in the direction of the crystallographic c-axis (thickness direction). For example, the thermal conductivity of a graphite single crystal can be up to about 1,920W/mK (theoretical) or 1,800W/mK (experimental) in the basal plane (crystallographic a-and b-axis directions), but less than 10W/mK (typically less than 5W/mK) along the crystallographic c-axis direction. Further, the plurality of grains or crystallites in the graphite particles are typically all oriented in different directions. Thus, natural graphite particles composed of a plurality of grains of different orientation exhibit an average behaviour between these two extremes (i.e. <100W/mK typically).

The constituent graphene planes of the graphite crystallites (typically 30nm-2 μm wide/long) can be bulked and extracted or isolated from the graphite crystallites to obtain individual graphene sheets of carbon atoms, provided that interplanar van der waals forces can be overcome. Isolated, individual graphene sheets of hexagonal carbon atoms are commonly referred to as single-layer graphene. A stack of a plurality of graphene planes bonded by van der waals force in the thickness direction with an inter-plane spacing of 0.3354nm is generally referred to as multilayer graphene. Multi-layer graphene platelets have up to 300 graphene planes (< 100nm in thickness), but more typically up to 30 graphene planes (< 10nm in thickness), even more typically up to 20 graphene planes (< 7nm in thickness), and most typically up to 10 graphene planes (often referred to as few-layer graphene in scientific community). Single-layer graphene sheets and multi-layer graphene sheets are collectively referred to as "nano-graphene platelets" (NGPs). Graphene sheets/platelets or NGP are a new class of carbon nanomaterials (2-D nanocarbons) that differ from 0-D fullerenes, 1-D CNTs, and 3-D graphites.

As early as 2002, our research group opened up the development of pristine graphene materials (isolated graphene oxide sheets) and related production methods: (1) Jang and w.c. huang, "Nano-scaled Graphene Plates [ ]]", U.S. Pat. No. 7,071,258 (07/04/2006), application filed on Ser. No. 10/21 of 2002; (2) Jang et al "Process for Producing Nano-scaled Graphene Plates [ method for Producing Nano-scaled Graphene Plates]", U.S. patent application Ser. No. 10/858,814 (06/03/2004); and (3) B.Z.Jang, A.Zhamu and J.Guo, "Process for Producing Nano-scaled plates and Nanocomposites [ Process for Producing nanoscale Platelets and Nanocomposites ]]", U.S. patent application Ser. No. 11/509,424 (08/25/2006). Historically, brodie demonstrated the synthesis of graphite oxide in 1859 for the first time by adding a portion of potassium chlorate to a slurry of graphite in fuming nitric acid. In 1898, staudenmaier improved on this procedure by using concentrated sulfuric acid and fuming nitric acid and adding chlorate in multiple aliquots during the reaction. This small change in procedure makes it significantly more practical to produce highly oxidized graphite in a single reaction vessel. In 1958 Hummers reported the most common use at presentThe method of (1): by adding in concentrated H ₂ SO ₄ Medium KMnO ₄ And NaNO ₃ Treated to oxidize graphite. However, these early works failed to isolate and identify fully expanded and isolated graphene oxide sheets. These studies also fail to disclose the isolation of native, non-oxidized monolayer or multilayer graphene sheets.

In actual practice (e.g., as shown in fig. 1 (a)), NGP is typically obtained by intercalating natural graphite particles 100 with a strong acid and/or an oxidizing agent to obtain graphite intercalation compound 102 (GIC) or Graphite Oxide (GO). The presence of chemical species or functional groups in the interstitial spaces between graphene planes serves to increase the inter-graphene spacing (d) ₀₀₂ As determined by X-ray diffraction) to thereby significantly reduce van der waals forces that would otherwise hold the graphene planes together along the c-axis direction. GIC or GO is most often produced by immersing natural graphite powder in a mixture of sulfuric acid, nitric acid (the oxidant) and another oxidant, such as potassium permanganate or sodium perchlorate. The resulting GIC (102) is actually some type of Graphite Oxide (GO) particles. The GIC or GO is then repeatedly washed and rinsed in water to remove excess acid, producing a graphite oxide suspension or dispersion containing discrete and visually identifiable graphite oxide particles dispersed in water. There are two process routes after this rinsing step:

route 1 involves the removal of water from the suspension to obtain "expandable graphite", which is essentially a mass of dry GIC or dry graphite oxide particles. When expandable graphite is exposed to temperatures in the typical range of 800 c to 1,050 c for about 30 seconds to 2 minutes, the GIC undergoes 30-300 times rapid volume expansion to form "graphite worms" (104), which are each an assemblage of expanded, yet interconnected, largely unisolated graphite flakes.

In route 1A, these graphite worms (expanded graphite or "network of interconnected/unseparated graphite flakes") can be recompressed to obtain flexible graphite sheets or foils (106), typically having a thickness in the range of 0.1mm (100 μm) to 0.5mm (500 μm). Alternatively, for the purpose of producing so-called "expanded graphite flakes" (108) which contain predominantly graphite flakes or platelets (and thus by definition are not nanomaterials) that are thicker than 100nm, the use of low intensity air mills or shears may be chosen to simply disintegrate the graphite worms. These expanded graphite sheets may be formed into paper-like graphite felt (110).

The expanded graphite worms, expanded graphite flakes, and recompressed masses of graphite worms (commonly referred to as flexible graphite flakes or foils) are all 3-D graphitic materials which are fundamentally different and distinctly different from 1-D nanocarbon materials (CNTs or CNFs) or 2-D nanocarbon materials (graphene sheets or platelets, NGPs). Flexible Graphite (FG) foil can be used as a heat spreader material, but exhibits a maximum in-plane thermal conductivity of typically less than 500W/mK (more typically < 300W/mK) and an in-plane electrical conductivity of no greater than 1,500s/cm. These low conductivity values are a direct result of: many defects, wrinkled or folded graphite flakes, interruptions or gaps between graphite flakes, and non-parallel flakes (e.g., SEM images in fig. 2). Many flakes are tilted at very large angles relative to each other (e.g., mis-orientation of 20-40 degrees).

In route 1B, expanded graphite is subjected to high intensity mechanical shearing (e.g., using an ultrasonic generator, a high shear mixer, a high intensity air jet mill, or a high energy ball mill) to form separate single and multi-layered graphene sheets (collectively referred to as NGPs, 112), as disclosed in our U.S. application No. 10/858,814. Single layer graphene can be as thin as 0.34nm, while multi-layer graphene can have a thickness of up to 100nm, but more typically less than 20 nm. The graphene sheets or platelets can then be made into graphene paper or film (114).

Route 2 requires ultrasonication of the graphite oxide suspension for the purpose of separating/isolating individual graphene oxide sheets from the graphite oxide particles. This is based on the following point: the spacing between graphene planes has increased from 0.3354nm in natural graphite to 0.6-1.1nm in highly oxidized graphite oxide, significantly reducing van der waals forces holding adjacent planes together. The ultrasonic power may be sufficient to further separate the graphene planar sheets to form separated, isolated, or discrete Graphene Oxide (GO) sheets. These graphene oxide sheets may then be chemically or thermally reduced to obtain "reduced graphene oxide" (RGO), typically having an oxygen content of 0.001-10% by weight, more typically 0.01-5% by weight, most typically and preferably less than 2% by weight.

For the purposes of defining the claims of the present application, NGPs include single and multi-layered discrete sheets/platelets of pristine graphene, graphene oxide, or Reduced Graphene Oxide (RGO). Pristine graphene has substantially 0% oxygen. RGO typically has an oxygen content of 0.001% to 5% by weight. Graphene oxide (including RGO) may have 0.001% -50% by weight oxygen.

It can be noted that flexible graphite foils (obtained by compressing or rolling expanded graphite worms) used in electronic device thermal management applications (e.g., as heat spreader materials) have the following major drawbacks: (1) As previously mentioned, flexible Graphite (FG) foils exhibit relatively low thermal conductivity, typically <500W/mK, and more typically <300W/mK. By impregnating the expanded graphite with resin, the resulting composite exhibits even lower thermal conductivity (typically < <200W/mK, more typically < 100W/mK). (2) Flexible graphite foil, without resin impregnated therein or coated thereon, has low strength, low stiffness, and poor structural integrity. The high tendency of flexible graphite foils to tear makes them difficult to handle during the manufacturing of heat sinks. In fact, flexible graphite sheets (typically 50-200 μm thick) are so "soft" that they do not have sufficient rigidity to make finned component material for finned heat sinks. (3) Another very subtle, largely overlooked or overlooked, but extremely important feature of FG foils is their high tendency to flake off, graphite flakes easily detaching from the FG sheet surface and scattering out to other parts of the microelectronic device. These highly conductive flakes (typically 1-200 μm in lateral dimension and >100nm thick) can lead to internal shorting and failure of the electronic device.

Similarly, solid NGPs (including discrete sheets/platelets of pristine graphene, GO, and RGO), when stacked into films, or paper sheets (114) of nonwoven aggregates using a papermaking process, typically do not exhibit high thermal conductivity unless the sheets/platelets are closely stacked and the films/papers are ultra-thin (e.g., <1 μm, which is mechanically weak). This is reported in our earlier U.S. patent application Ser. No. 11/784,606 (4/9/2007). However, ultra-thin films or sheets (< 10 μm) are difficult to mass produce and difficult to handle when trying to incorporate these thin films into a heat spreader material. Generally, paper-like structures or felts made from platelets of graphene, GO, or RGO (e.g., those paper sheets prepared by vacuum-assisted filtration processes) exhibit many defects, wrinkled or folded graphene sheets, breaks or gaps between platelets, and non-parallel platelets (e.g., SEM images in fig. 3 (B)), resulting in relatively poor thermal conductivity, low electrical conductivity, and low structural strength. These papers or aggregates of discrete NGP, GO or RGO platelets alone (without a resin binder) also have a tendency to flake off, emitting conductive particles into the air.

Another prior art graphite material is pyrolytic graphite film, typically thinner than 100 μm. The process starts at a carbonization temperature of 400 ℃ to 1,500 ℃ at 10 to 15Kg/cm ² For 10 to 36 hours at a typical pressure of (2,500 ℃ to 3,200 ℃ followed by 100 to 300Kg/cm of carbonized material ² Is subjected to the graphitization treatment at an ultra-high pressure for 1 to 24 hours to form a graphite film. Maintaining such ultra-high pressures at such ultra-high temperatures is technically extremely challenging. This is a difficult, slow, lengthy, energy consuming and extremely expensive process. In addition, it has been difficult to produce pyrolytic graphite films thinner than 10 μm or thicker than 100 μm from polymers such as polyimide. The problem associated with such thicknesses is inherent with such materials because they are difficult to form ultra-thin (C.) (R.) (<10 μm) and thick film (>100 μm) while still maintaining an acceptable level of polymer chain orientation and mechanical strength required for proper carbonization and graphitization.

The second type of pyrolytic graphite is produced by pyrolysis of hydrocarbon gases in a vacuum followed by deposition of carbon atoms onto the substrate surface. This vapor phase condensation of cracked hydrocarbons is essentially a Chemical Vapor Deposition (CVD) process. In particular, highly Oriented Pyrolytic Graphite (HOPG) is a material produced by subjecting CVD-deposited pyrolytic carbon to uniaxial pressure at very high temperatures (typically 3,000-3,300 ℃). This requires a combined and simultaneous mechanical compression and ultra-high temperature thermomechanical treatment in a protective atmosphere for an extended period of time; a very expensive, energy consuming, time consuming and technically challenging process. The process requires ultra high temperature equipment (with high vacuum, high pressure or high compression supplies) which is not only very expensive to manufacture but also very expensive and difficult to maintain. Even with such extreme processing conditions, the resulting HOPG still has many defects, grain boundaries and misorientations (adjacent graphene planes are not parallel to each other), resulting in less than satisfactory in-plane properties. Typically, the best prepared HOPG sheets or blocks typically contain many poorly aligned grains or crystals and a large number of grain boundaries and defects.

Similarly, the recent reports have passed through hydrocarbon gases (e.g., C) ₂ H ₄ ) Graphene thin films on Ni or Cu surfaces prepared by catalytic CVD (A)<2 nm) is not a single-grain crystal but a polycrystalline structure having many grain boundaries and defects. In the case where Ni or Cu is a catalyst, carbon atoms obtained via decomposition of hydrocarbon gas molecules at 800 ℃ to 1,000 ℃ are deposited onto the Ni or Cu foil surface to form sheets of single or few layer graphene that are polycrystalline. The size of the grains is typically much less than 100 μm, and more typically less than 10 μm in size. These graphene thin films (which are optically transparent and electrically conductive) are intended for applications such as touch screens (to replace indium tin oxide or ITO glass) or semiconductors (to replace silicon, si). Furthermore, ni-or Cu-catalyzed CVD processes are not suitable for depositing more than 5 graphene planes (typically<2 nm), over 5 graphene planes, the underlying Ni or Cu catalyst can no longer provide any catalytic effect. There is no experimental evidence that CVD graphene layers thicker than 5nm are possible. Both CVD graphene films and HOPG are very expensive.

The above discussion clearly shows that each of the prior art methods or processes for producing graphene and graphite thin films have major drawbacks. Therefore, the alloy has the characteristics (such as electrical conductivity, thermal conductivity, and gold) required for the current collectorThere is an urgent need for a new class of carbon nanomaterials that are comparable or superior to graphene in terms of contact resistance of the foil), strength, and electrolyte compatibility with the intended battery or supercapacitor. It is also necessary to be able to produce these materials in a more cost effective, faster, more scalable, and more environmentally friendly manner. The production process of such new carbon nanomaterials must require reduced amounts of undesirable chemicals (or the elimination of these chemicals altogether), reduced processing times, reduced energy consumption, reduced or eliminated entry of undesirable chemical species into the exhaust system (e.g., sulfuric acid) or into the air (e.g., SO) ₂ And NO ₂ ) The outflow amount of (c).

Humic Acid (HA) is an organic substance commonly found in soil and can be extracted from soil using a base such as KOH. HA can also be extracted from a class of coals known as leonardite, which is a highly oxidized version of lignite. HA extracted from leonardite contains many oxygen-containing groups (e.g., carboxyl groups) located at the center of graphene-like molecules (SP of hexagonal carbon structure) ² Core) around the rim. This material is somewhat similar to Graphene Oxide (GO) produced by the oxidation of natural graphite by strong acids. HA HAs a typical oxygen content of 5 to 42% by weight (the other main elements are carbon, hydrogen and nitrogen). Examples of the molecular structure of humic acids with various components (including quinone, phenol, catechol, and sugar moieties) are shown in scheme 1 (source: stevenson F.J. "Humus Chemistry: genetics, composition, reactions [ Humus Chemistry: origin, composition, reaction]”，John Wiley&Sons [ John Willi parent-child publishing Co]1994), new york).

Non-aqueous solvents for humic acids include polyethylene glycol, ethylene glycol, propylene glycol, alcohols, sugar alcohols, polyglycerols, glycol ethers, amine-based solvents, amide-based solvents, alkylene carbonates, organic acids, or inorganic acids.

The invention also provides a method forMethod for producing highly oriented humic acid films (with or without externally added graphene sheets) and humic acid derived graphite films having a thickness of from 2nm to 30 μm (more typically and preferably from 5nm to 10 μm, even more typically from 10nm to 2 μm) and a physical density of not less than 1.3g/cm ³ (Up to 2.2 g/cm) ³ ). This film is chemically bonded to the surface of the metal foil. In certain embodiments, the method comprises:

(a) Preparing a dispersion of Humic Acid (HA) or chemically functionalized humic acid (CHA) flakes dispersed in a liquid medium, wherein the HA flakes contain an oxygen content higher than 5% by weight or the CHA flakes contain a non-carbon element content higher than 5% by weight; ( In certain preferred embodiments, the HA or CHA dispersion further contains graphene sheets or molecules dispersed therein, and the ratio of HA to graphene or CHA to graphene is from 1/100 to 100/1. The graphene sheets may be selected from pristine graphene, graphene oxide, reduced graphene oxide, fluorinated graphene, brominated graphene, iodinated graphene, boron-doped graphene, nitrogen-doped graphene, chemically functionalized graphene, or combinations thereof. )

(b) Dispensing and depositing the HA or CHA dispersion onto at least one major surface of a metal foil (e.g., a Cu foil) to form a wet layer of HA or CHA, wherein the dispensing and depositing procedure comprises subjecting the dispersion to orientation-inducing stress; ( This orientation-controlling stress (typically including shear stress) enables the alignment of HA/CHA sheets (or plate-like molecules) and graphene sheets (if present) along the planar direction of the metal foil substrate surface (e.g., cu foil). Proper alignment of the HA/CHA and graphene sheets during subsequent thermal treatment is necessary for chemical linking or incorporation between two or more HA/CHA sheets, or between HA/CHA sheets and graphene sheets. )

(c) Partially or completely removing the liquid medium from the wet layer of HA or CHA to form a composite having hexagonal carbon planes and an interplanar spacing d between 0.4nm and 1.3nm as determined by X-ray diffraction ₀₀₂ A dried HA or CHA layer of (a); and

(d) Heat treating the dried HA or CHA layer at a first heat treatment temperature above 80 ℃ for a sufficient period of time to produce a highly oriented humic acid film containing interconnected or combined HA or CHA sheets substantially parallel to each other. The humic acid film is also chemically bonded to the surface of the metal foil. These HA/CHA sheets have also typically been thermally reduced. This highly oriented humic acid film of reduced HA or CHA may be subjected to a further step of compression against a metal foil.

The process (with or without a compression step) may comprise a further step (e): further heat treating the humic acid film of the combined and reduced HA or CHA at a second heat treatment temperature higher than the first heat treatment temperature for a sufficient period of time to produce a film having an inter-planar spacing d of less than 0.4nm ₀₀₂ And a graphite film having an oxygen content or non-carbon element content of less than 5% by weight; and (f) compressing the graphite film (e.g., against a Cu foil) to produce a highly conductive graphite film bonded to the metal foil.

In an embodiment, step (e) comprises at a second heat treatment temperature (typically higher than the first heat treatment temperature)>Heat treating the highly oriented humic acid film at 300 ℃) for a period of time sufficient to maintain the inter-planar spacing d ₀₀₂ To a value from 0.3354 to 0.36nm and to reduce the oxygen or non-carbon content to less than 0.5% by weight. In a preferred embodiment, the second (or final) heat treatment temperature comprises at least one temperature selected from: (A) 100 ℃ to 300 ℃, (B) 300 ℃ to 1,500 ℃, (C) 1,500 ℃ to 2,500 ℃, and/or (D) 2,500 ℃ to 3,200 ℃. Preferably, the second heat treatment temperature comprises a temperature in the range of 300 ℃ to 1,500 ℃ for at least 1 hour, and then a temperature in the range of 1,500 ℃ to 3,200 ℃ for at least another 1 hour.

Typically, if both the first and second heat treatment temperatures are below 1,500 ℃, the Highly Oriented Humic Acid (HOHA) film also contains planar molecules that are characteristic of humic acid molecules. Highly Oriented Humic Acid (HOHA) films contain chemically bonded and merged hexagonal carbon planes, which are HA/CHA or combined HA/CHA-graphene planes. These planes (hexagonal structure carbon atoms with a small number of oxygen-containing groups) are parallel to each other.

If exposed to a Heat Treatment Temperature (HTT) of 1,500 ℃ or higher for a sufficient period of time, the HOHA film typically no longer contains any significant amount of humic acid molecules, and substantially all of the HA/CHA platelets/molecules have been converted to graphene-like or graphene oxide hexagonal carbon planes that are parallel to each other. The transverse dimensions (length or width) of these planes are enormous, typically several times or even orders of magnitude larger than the largest dimension (length/width) of the starting HA/CHA sheet. The HOHA of the present invention is essentially all "giant hexagonal carbon crystals" or "giant planar graphene-like layers" that constitute graphene-like planes that are substantially parallel to each other. This is a unique and new class of materials that have not previously been discovered, developed or suggested to be present.

Oriented HA/CHA layers (HOHA films with HTT no >1,500 ℃) are themselves a very unique and novel class of materials, which surprisingly have large cohesion (self-binding, self-polymerization and self-crosslinking capabilities). These features have not been previously taught or suggested in the prior art.

The above paragraphs were written to describe one type of current collector obtained by heat-treating a metal film incorporating HA or an HA/graphene mixture into a two-or three-layer laminate. The HA or HA/graphene layer was not peeled from the metal foil and heat treated separately (without the metal foil). The resulting current collector contains no binder resin or adhesive. This type is referred to herein as a type a current collector. This type of current collector may be heat treated up to a maximum temperature close to the melting point of the underlying metal foil. However, certain metal foils (e.g., cu, ti, and steel) appear to be capable of catalyzing the chemical connection between HA sheets or between HA and graphene, enabling the formation of larger HA/graphene domains and fewer defects and resulting in higher thermal and electrical conductivity and structural integrity (which otherwise cannot be achieved without invoking much higher heat treatment temperatures).

The preparation of type B current collectors is described in the following two paragraphs:

alternatively, the above procedure from (a) to (d) or (e) may be carried out by: the dispersion of HA or HA/graphene mixture is deposited onto the surface of a plastic film or glass and, after removal of the liquid, the resulting dried film is peeled off the plastic film or glass so that the film can be subsequently heat treated at any desired temperature. The highly oriented HA film (after heat treatment at temperatures from 80 ℃ to 1,500 ℃) or the derivatized graphite film (after heat treatment at temperatures from 1,500 ℃ to 3,200 ℃) is then bonded as a free standing film to one or both major surfaces of a metal foil (e.g., a Cu or Al foil) using a binder resin or adhesive. Such type B current collectors (obtained at comparable final heat treatment temperatures) have lower in-plane thermal conductivity, lower in-plane electrical conductivity, higher interlayer contact resistance, and are less durable (more easily delaminated) in the true liquid electrolyte environment inside a battery or supercapacitor, compared to type a current collectors, where highly oriented HA films or highly conductive graphite films derived therefrom are prepared by depositing a thin film of HA or HA/graphene directly to the surface of a metal foil and chemically bonding to this surface without the use of a binder.

To partially alleviate these problems, binder materials that are more conductive than typical binder resins (e.g., PVDF, SBR, etc., commonly used in the lithium battery and supercapacitor industries) are selected for use. These include intrinsically conductive polymers (e.g., polyaniline, polypyrrole, polythiophene, etc.), pitch (e.g., isotropic pitch, mesophase pitch, etc.), amorphous carbon (e.g., by chemical vapor infiltration), or carbonized resins (heat treating the current collector after the free-standing graphite layer is bonded to the metal foil, converting the resin binder into a carbon binder in situ).

The following description applies to both type a and type B current collectors.

For certain HA or CHA molecules containing significant amounts of-OH and/or-COOH groups on the edges and/or plane of the HA/CHA platelets (e.g., having an oxygen content of between 20% and 47% by weight, preferably between 30% and 47%), step (a) entails dispersing the HA/CHA platelets or molecules in a liquid medium, which may be water or a mixture of water and alcohol.

When the volume fraction or weight fraction of HA/CHA exceeds a threshold value, the resulting dispersion is found to contain a liquid crystalline phase. Preferably, prior to step (b), the HA/CHA suspension (dispersion) contains an initial volume fraction of HA/CHA platelets, said initial volume fraction exceeding a critical or threshold volume fraction for the formation of a liquid crystalline phase. We have observed that this critical volume fraction typically corresponds to a HA/CHA weight fraction in the range of from 0.2% to 5.0% by weight of HA/CHA flakes in the dispersion. However, such low HA/CHA content ranges are not particularly well suited for forming the desired films using scalable processes such as casting and coating. The ability to produce thin films by casting or coating is highly advantageous and desirable because large scale and/or automated casting or coating systems are readily available and these methods are known to be reliable for producing polymer films of consistently high quality. Therefore, we continue to conduct intensive and extensive research into the suitability of dispersions containing a liquid crystalline phase based on HA/CHA for casting or coating. We have found that by concentrating the dispersion to increase the HA/CHA content from the range of 0.2 to 5.0% by weight to the range of 4 to 16% by weight of HA/CHA sheets, we obtain a dispersion that is highly suitable for large-scale production of thin graphene films. Most notably and quite unexpectedly, the liquid crystalline phase is not only retained, but often reinforced, making it more feasible to orient the HA/CHA sheet in a preferred orientation during the casting or coating procedure. In particular, HA/CHA sheets in the liquid crystalline state containing 4 to 16% by weight of HA/CHA sheets have the highest tendency to become easily oriented under the influence of shear stress generated by commonly used casting or coating methods.

Thus, in step (b), the HA/CHA suspension is preferably formed into a thin film layer under the influence of shear stress that promotes laminar flow. An example of such a shearing procedure is the casting or coating of a film of HA/CHA suspension using a slot die coater. This procedure is similar to applying a layer of polymer solution to a solid substrate. When the film is formed, or when there is relative motion between the roller/blade/wiper and the supporting substrate at a sufficiently high relative motion speed, the roller, "doctor blade" or wiper generates shear stress. Quite unexpectedly and significantly, such shearing action enables the planar HA/CHA sheets to align well, for example, in the shearing direction. Further unexpectedly, such molecular alignment or preferred orientation is not disrupted when the liquid component of the HA/CHA suspension is subsequently removed to form a well-packed layer of at least partially dried highly aligned HA/CHA sheets. The dried layer has a high birefringence coefficient between the in-plane direction and the perpendicular-to-plane direction.

The present invention includes the discovery of a simple amphiphilic self-assembly method for making HA/CHA based films with desirable hexagonal planar orientation. HA, containing between 5% and 46% by weight of oxygen, can be considered as a negatively charged amphiphilic molecule due to the combination of its hydrophilic oxygen-containing functional groups and hydrophobic basal planes. For CHA, the functional groups can be made hydrophilic or hydrophobic. The successful preparation of HA/CHA films with unique hexagonal, graphene-like planar orientation does not require complex procedures. Rather, it is achieved by tailoring the HA/CHA synthesis and manipulating the liquid crystal phase formation and deformation behavior such that the HA/CHA sheet is capable of self-assembly in the liquid crystal phase.

The HA/CHA suspension was characterized using Atomic Force Microscopy (AFM), raman spectroscopy and FTIR to confirm its chemical state. Finally, the presence of lyotropic mesomorphic states of HA plates (liquid crystalline HA phase) in aqueous solution was confirmed by cross-polarized light observation.

Two main aspects are considered to determine whether a 1-D or 2-D species can form a liquid crystal phase in a liquid medium: aspect ratio (length/width/diameter to thickness ratio) and sufficient dispersibility or solubility of the material in a liquid medium. HA or CHA sheets are characterized by high anisotropy, as well as monoatomic or small atomic thickness (t) and generally micron-sized lateral width (w). According to ozagre's theory, high aspect ratio 2D sheets can form liquid crystals in a dispersion when their volume fraction exceeds a critical value:

V _c 4t/w (equation 1)

Assuming a graphene-like plane with a thickness of 0.34nm and a width of 1 μm, the required critical volume would be V _c ≈4t/w＝4x0.34/1,000＝1.36x10 ^-3 =0.136%. However, pristine graphene sheets are insoluble in water due to their pi-pi stacking attraction and poorly dispersible in common organic solvents (maximum volume fraction, V) _m About 0.7x10 in N-methylpyrrolidone (NMP) ^-5 And about 1.5x10 in ortho-dichlorobenzene ^-5 ). Fortunately, the molecular structure of HA or CHA can be made to exhibit good dispersibility in water and polar organic solvents (e.g., alcohols, N-Dimethylformamide (DMF) and NMP) due to the large number of oxygen-containing functional groups attached to its edges. Naturally occurring HA (e.g., HA from coal) is also highly soluble in non-aqueous solvents of humic acid, including polyethylene glycol, ethylene glycol, propylene glycol, alcohols, sugar alcohols, polyglycerols, glycol ethers, amine-based solvents, amide-based solvents, alkylene carbonates, organic acids, inorganic acids, or mixtures thereof.

Although it is speculated from theoretical predictions that the critical volume fraction of HA/CHA may be below 0.2% or the critical weight fraction below 0.3%, we have observed that the critical weight fraction of HA/CHA platelets forming liquid crystals is significantly higher than 0.4% by weight. When the weight fraction of HA/CHA platelets is in the range of 0.6% to 5.0%, the most stable liquid crystals are present, which leads to high stability over a wide temperature range. To investigate the effect of HA/CHA size on the formation of its liquid crystal structure, HA/CHA samples were prepared using a pH-assisted selective sedimentation technique. The lateral dimensions of the HA/CHA sheet were evaluated by Dynamic Light Scattering (DLS) via three different measurement modes as well as AFM.

During the study of HA/CHA liquid crystals we have an unexpected but very important finding: the liquid crystalline phase of the HA/CHA sheet in water and other solvents can be easily disrupted or destroyed by mechanical disturbances (e.g., mechanical mixing, shearing, turbulence, etc.). The mechanical stability of these liquid crystals can be significantly improved if the concentration of HA/CHA platelets is gradually increased to more than 5% (preferably from 5 to 16% by weight) by careful removal (e.g. evaporation) of the liquid medium without mechanically disturbing the liquid crystal structure. We further observed that, with the HA/CHA weight fraction in this 5% -16% range, HA/CHA platelets are particularly well suited for forming the desired orientation during casting or coating to form films.

Thermodynamically, the process of self-assembly of amphiphilic HA/CHA into a liquid crystal phase is the interaction of enthalpy change (Δ H) and entropy change (Δ S), e.g., isoShown in formula (2): Δ G _{Self-assembly} ＝ΔH _{Self-assembly} -TΔS _{Self-assembly} (2)

Previous studies of the thermodynamic driving force for amphiphilic self-assembly into liquid crystal phases have shown that the contribution of entropy plays a dominant role, while enthalpy changes are in most cases disadvantageous. The ozaeger theory predicts that high aspect ratio particles can form liquid crystal phases above the critical volume fraction due to a net increase in entropy, since the loss of orientation entropy is compensated for by increased translational entropy. In particular, higher aspect ratio particles favor the formation of long-range liquid crystalline phases. Another possible cause of the HA/CHA aspect ratio effect may be structural corrugation of the HA/CHA sheet in solvent, since the restoring force from bending the sheet is much weaker than the restoring force along the sheet. It was found that the extent of the HA/CHA corrugated morphology in solvent could be further enhanced if its aspect ratio was increased. This corrugated configuration will significantly affect the intramolecular and intermolecular interactions of HA/CHA in suspension.

To achieve long range order in aqueous dispersions, well expanded HA/CHA sheets with strong long range electrostatic repulsion are needed. The formation of liquid crystal structures from colloidal particles typically requires a delicate balance of long-range repulsive forces (e.g., electrostatic forces) and short-range attractive forces (e.g., van der waals and pi-pi interactions). If the long-range repulsive forces are not strong enough to overcome the short-range attractive forces, aggregation of colloidal particles or weak formation of lyotropic liquid crystals with only small periodicity will inevitably occur. In HA/CHA aqueous dispersions, the electrical bilayer formed by ionized oxygen functional groups provides a long range repulsive interaction. Although the HA/CHA plate still contains a substantial portion of hydrophobic domains, attractive π - π interactions and van der Waals forces can be effectively overcome by modulating the remote electrostatic repulsive forces

The chemical composition of HA/CHA plays an important role in tailoring the electrostatic interactions in aqueous or organic solvent dispersions. An increase in surface charge density will result in an increase in the strength of electrostatic repulsion versus attraction. The ratio of aromatic and oxygen-containing domains can be readily adjusted by the level of hexagonal carbon plane oxidation or chemical modification. Fourier transform infrared spectroscopy (FTIR-ATR) results of the attenuated total reflectance mode of HA/CHA indicate the presence of oxidized species (hydroxyl, epoxy and carboxyl) on the HA/CHA surface. Thermogravimetric analysis (TGA) in nitrogen was used to probe the oxygen functional group density on the HA/CHA surface. For highly oxidized HA, a mass loss of about 28% by weight was found at about 250 ℃ and was attributed to the decomposition of unstable oxygen-containing species. Below 160 c, a mass loss of about 16wt% was observed, corresponding to desorption of physically absorbed water. X-ray photoelectron spectroscopy (XPS) results of HA showed an atomic ratio of C/O of about 1.9. This indicates that HA HAs a relatively high density of oxygen functional groups. Furthermore, we have also prepared HA containing lower density oxygen functional groups by simply varying the thermal or chemical reduction time and temperature of heavily oxidized HA (e.g. from leonardite). We have observed that the oxygen weight fraction of the liquid crystal can be found to be preferentially in the range of 5% -40%, more preferably 5% -30%, and most preferably 5% -20%.

Colloidal interactions between HA sheets can be significantly affected by ionic strength, since the debye screening length (κ -1) can be effectively increased by reducing the free ion concentration around the HA sheet. The electrostatic repulsion of HA liquid crystals in water may decrease with increasing salt concentration. As a result, more water is drained from the HA interlayer space with a concomitant decrease in d-spacing. Therefore, the ionic impurities in the HA dispersion should be sufficiently removed, since it is a crucial factor affecting the formation of the liquid crystal structure of HA.

However, we have also found that the incorporation of some small amount of polymer (up to 10% by weight, but preferably up to 5% by weight, and most preferably only up to 2%) can help to stabilize the liquid crystalline phase when the HA/CHA dispersion is subjected to a casting or coating operation. By appropriate functional groups and concentrations, GO/CFG orientation in the resulting film can be enhanced. This has never been taught or suggested in previous publications or patent documents.

The dried HA/CHA layer may then be subjected to a heat treatment. A suitably programmed heat treatment program may involve at least two heat treatment temperatures (a first temperature for a period of time and then raised to and held at a second temperature for another period of time), or any other combination of at least two Heat Treatment Temperatures (HTTs) involving an initial treatment temperature (first temperature) and a final HTT (higher than the first temperature).

The first heat treatment temperature is for chemical ligation and thermal reduction of HA/CHA and is carried out at a first temperature >80 ℃ (may be up to 1,000 ℃, but preferably up to 700 ℃, and most preferably up to 300 ℃). This is referred to herein as scheme 1:

scheme 1 (up to 300 ℃): within this temperature range (initial chemical ligation and thermal reduction protocol), chemical combination, polymerization (edge-to-edge merging), and crosslinking begin to occur between adjacent HA/CHA sheets. Multiple HA/CHA sheets are stacked side-by-side and edge-to-edge and chemically bonded together to form an integrated layer of graphene oxide-like entities. Furthermore, the HA/CHA layer undergoes primarily thermally induced reduction reactions, resulting in a reduction of the oxygen content to about 5% or less. This treatment resulted in a decrease in the inter-graphene spacing from about 0.8-1.2nm (as dried) to about 0.4nm, and an increase in the in-plane thermal conductivity from about 100W/mK to 500W/mK. Even in this low temperature range, some chemical bonding between the HA/CHA sheets occurs. The HA/CHA sheets remain well aligned, but the graphene interplanar spacing remains relatively large (0.4 nm or greater). Many O-containing functional groups remain.

The highest or final HTT experienced by the GO species can be divided into three different HTT regimes:

scheme 2 (300 ℃ -1,500 ℃): in this predominantly chemically linked scheme, additional thermal reduction and extensive chemical assembly, polymerization and crosslinking occur between adjacent HA/CHA sheets. Chemical linkage between HA/CHA and graphene sheets (e.g., GO sheets), if present, can also occur. After chemical linking, the oxygen content is reduced to typically below 1%, resulting in a reduction of the inter-graphene spacing to about 0.35nm. This means that some initial graphitization has already been initiated at such low temperatures, in sharp contrast to conventional graphitizable materials (e.g., carbonized polyimide films) which typically require temperatures as high as 2,500 ℃ to initiate graphitization. This is another significant feature of the HOHA membrane of the present invention and the method of producing the same. These chemical bonding reactions result in an increase in-plane thermal conductivity to 850-1,250W/mK, and/or an increase in-plane electrical conductivity to 3,500-4,500S/cm.

Scheme 3 (1,500 ℃ -2,500 ℃): in this ordered and re-graphitized approach, extensive graphitization or graphene plane merging occurs, resulting in a significant improvement in structural order. As a result, the oxygen content is reduced to typically 0.01% and the inter-graphene spacing is reduced to about 0.337nm (depending on the actual HTT and duration, a degree of graphitization from 1% to about 80% is achieved). The improved degree of order is also reflected by an increase in-plane thermal conductivity to >1,300-1,500w/mK, and/or an increase in-plane electrical conductivity to 5,000-7,000s/cm.

Scheme 4 (above 2,500 ℃): in this recrystallization and perfection protocol, substantial movement and elimination of grain boundaries and other defects occurs, resulting in the formation of nearly perfect single or polycrystalline graphene crystals with large grains, which can be orders of magnitude larger than the original grain size of the starting HA/CHA sheet. Oxygen content is substantially eliminated, typically 0.01% to 0.1%. The inter-graphene spacing is reduced to about 0.3354nm (degree of graphitization from 80% to close to 100%), corresponding to that of a perfect graphite single crystal. Very interestingly, graphene polycrystals have all graphene planes closely packed and bonded, and all planes are aligned in one direction, perfectly oriented. I.e., by subjecting pyrolytic graphite to ultra-high pressure (300 Kg/cm) simultaneously ² ) HOPG produced at ultra-high temperatures (3,400 ℃) also did not produce such a perfectly oriented structure. Highly oriented graphene structures can achieve such highest degrees of integrity at significantly lower temperatures and ambient (or slightly higher compressive) pressures. The structures thus obtained exhibit a structure ranging from 1,500 up to a little bit>An in-plane thermal conductivity of 1,700W/mK, and an in-plane electrical conductivity in a range from 15,000 to 20,000S/cm.

The highly oriented HA-derived structures of the invention may be obtained by heat treating the HA/CHA layer with a temperature program covering at least the first protocol (typically requiring 1-24 hours in this temperature range), more typically the first two protocols (1-10 hours preferred), still more typically the first three protocols (preferably 0.5-5 hours in protocol 3), and most typically all four protocols (protocol 4 lasts 0.5 to 2 hours, which may be carried out to achieve the highest conductivity).

X-ray diffraction patterns were obtained with an X-ray diffractometer equipped with CuKcv radiation. The shift and broadening of the diffraction peaks were calibrated using silicon powder standards. Using the Mering equation, d ₀₀₂ 0.3354g (= 0.344 g) and graphitization degree g calculated by X-ray diagram, where d is ₀₀₂ Is the spacing between graphite or graphene crystal layers in nm. Only when d ₀₀₂ Equal to or less than about 0.3440nm, this equation is valid. Having a d above 0.3440nm ₀₀₂ Reflects oxygen-containing functional groups that act as spacers to increase the inter-graphene spacing (e.g., -OH, on graphene-like planar surfaces,>O and-COOH).

Another structural index that can be used to characterize the order of the HOHA-derived graphite films of the present invention and conventional graphite crystals is the "mosaic spread", which is represented by the full width at half maximum of the rocking curve (X-ray diffraction intensity) of the (002) or (004) reflection. This degree of order characterizes the graphite or graphene crystal size (or grain size), the amount of grain boundaries and other defects, and the preferred degree of grain orientation. An almost perfect single crystal of graphite is characterized by a mosaic expansivity value of 0.2-0.4. Most of our HOHA-derived graphite samples had mosaic spread values within this range of 0.2-0.4 (if produced with a Heat Treatment Temperature (HTT) of not less than 2,500 ℃). However, if the HTT is between 1,500 ℃ and 2,500 ℃, some values are in the range of 0.4-0.7; and some values are in the range of 0.7-1.0 if the HTT is between 300 ℃ and 1,500 ℃.

HA or graphene can be functionalized by various chemical pathways. In a preferred embodiment, the resulting functionalized HA or functionalized graphene (collectively denoted Gn) may broadly have the following formula (e):

[Gn]--R _m

where m is the number of different functional group types (typically between 1 and 5), R is selected from SO ₃ H、COOH、NH ₂ OH, R 'CHOH, CHO, CN, COCl, halide, COSH, SH, COOR', SR ', siR' ₃ 、Si(--OR'--) _y R' ₃ -y、Si(--O--SiR' ₂ -)OR'、R”、Li、AlR' ₂ 、Hg--X、TlZ ₂ And Mg- -X; wherein y is an integer equal to or less than 3, R 'is hydrogen, alkyl, aryl, cycloalkyl or aralkyl, cycloaryl or poly (alkylether), R' is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl or cycloaryl, X is halide, and Z is carboxylate or trifluoroacetate.

The functional group-NH provided that a polymer such as an epoxy resin and HA or graphene sheets can be combined to make a coating composition ₂ Are of particular interest. For example, a commonly used curing agent for epoxy resins is Diethylenetriamine (DETA), which may have 2 or more-NH groups ₂ A group. -NH ₂ One of the groups may be bonded to the edge or surface of the graphene sheet, and the remaining unreacted-NH ₂ The groups are available for subsequent reaction with an epoxy resin. This arrangement provides good interfacial bonding between the HA (or graphene) sheets and the resin additive.

Other useful chemical functional groups or reactive molecules may be selected from the group consisting of: amidoamines, polyamides, aliphatic amines, modified aliphatic amines, cycloaliphatic amines, aromatic amines, anhydrides, ketimines, diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), polyethylenepolyamines, polyamine epoxy adducts, phenolic hardeners, non-brominated curatives, non-amine curatives, and combinations thereof. These functional groups are multifunctional, having the ability to react with at least two chemical species from at least two ends. Most importantly, they can be bonded to the edge or surface of graphene or HA using one of their ends and can react with the resin at one or both of the other ends during a subsequent curing stage.

Gn described above]--R _m Further functionalization may be possible. The resulting CFG includes compositions having the formula: [ Gn)]--A _m Wherein A is selected from OY, NHY, O = C- -OY, P = C- -NR ' Y, O = C- -SY, O = C- -Y, - - -CR '1- -OY, N ' Y or C ' Y, and Y is a suitable functional group of a protein, peptide, amino acid, enzyme, antibody, nucleotide, oligonucleotide, antigen, or a substrate for an enzyme, an inhibitor for an enzyme, or a transition state analogue of a substrate for an enzyme or is selected from R ' - -OH, R ' - -NR ' ₂ 、R'SH、R'CHO、R'CN、R'X、R'N ⁺ (R') ₃ X ^- 、R'SiR' ₃ 、R'Si(--OR'--) _y R' _3-y 、R'Si(--O--SiR' ₂ --)OR'、R'--R”、R'--N--CO、(C ₂ H ₄ O--) _w H、(--C ₃ H ₆ O--) _w H、(--C ₂ H ₄ O) _w --R'、(C ₃ H ₆ O) _w -R', and w is an integer greater than 1 and less than 200.

The HA and/or graphene sheets may also be functionalized to produce a composition having the formula:

[Gn]--[R'--A] _m

wherein m, R' and A are as defined above. The compositions of the invention also include CHA having certain cyclic compounds adsorbed thereon. These include compositions of matter having the formula:

[Gn]--[X--R _a ] _m

wherein a is zero or a number less than 10, X is a polynuclear aromatic moiety, a polyhalogenic aromatic moiety or a metallopolyhalogenic aromatic moiety, and R is as defined above. Preferred cyclic compounds are planar. More preferred cyclic compounds for adsorption are porphyrins and phthalocyanines. The adsorbed cyclic compound may be functionalized. Such compositions include compounds having the formula: [ Gn)]--[X--A _a ] _m

Wherein m, a, X and A are as defined above.

The functionalized HA or graphene of the present invention can be prepared directly by sulfonation, electrophilic addition to the surface of the deoxy GO, or metallization. The graphene or HA sheets may be processed prior to contacting with the functionalizing agent. Such treatment may include dispersing graphene or HA sheets in a solvent. In some examples, the sheets may then be filtered and dried prior to contacting. One particularly useful type of functional group is carboxylic acid moieties that are naturally present on the surface of HA if it is prepared by the acid intercalation route discussed above. If additional amounts of carboxylic acid are needed, the HA chips may be subjected to chlorate, nitric acid, or ammonium persulfate oxidation.

Carboxylic acid functionalized graphene sheets are particularly useful because they can serve as a starting point for preparing other types of functionalized graphene or HA sheets. For example, an alcohol or amide can be readily linked to an acid to give a stable ester or amide. If the alcohol or amine is part of a di-or multifunctional molecule, the linkage via O-or NH-leaves other functional groups as pendant groups. These reactions can be carried out using any method developed for esterification with alcohols or amination of carboxylic acids with amines as is known in the art. Examples of such methods can be found in g.w. anderson et al, j.amer.chem.soc. [ chem. ]96,1839 (1965), which is incorporated herein by reference in its entirety. The amino groups can be introduced directly onto the graphite fibrils by: the fibrils are treated with nitric and sulfuric acid to obtain nitrated fibrils, which are then chemically reduced with a reducing agent such as sodium dithionite to obtain amino-functionalized fibrils.

We have found that the aforementioned functional groups can be attached to the HA or graphene sheet surface or edge for one or several of the following purposes: (a) Improving the dispersion of graphene or HA in a desired liquid medium; (b) Enhancing the solubility of graphene or HA in a liquid medium such that a sufficient amount of graphene or HA sheets can be dispersed in the liquid, beyond the critical volume fraction for liquid crystal phase formation; (c) Enhancing the film forming ability so that a thin film of originally discrete graphene or HA sheets can be coated or cast; (d) Improving the orientation capability of graphene or HA sheets due to changes to flow behavior; and (e) the ability to enhance graphene or HA sheets to chemically link and merge into larger or wider graphene planes.

The present invention also provides a rechargeable battery containing the graphene oxide thin film-bonded metal foil of the present invention as an anode current collector and/or a cathode current collector. This may be any rechargeable battery, such as a zinc air cell, a nickel metal hydride cell, a sodium ion cell, a metal sodium cell, a magnesium ion cell, a metal magnesium cell, to name a few. The battery of the invention may be a rechargeable lithium battery containing a monolithic graphene layer as an anode current collector or a cathode current collector, which may be a lithium-sulfur cell, a lithium-selenium cell, a lithium-sulfur/selenium cell, a lithium-ion cell, a lithium-air cell, a lithium-graphene cell, or a lithium-carbon cell. Another embodiment of the invention is a capacitor comprising the current collector of the invention as an anode current collector or a cathode current collector, the capacitor being a symmetric supercapacitor, an asymmetric supercapacitor cell, a hybrid supercapacitor-battery cell, or a lithium ion capacitor cell.

By way of example, the present invention provides a rechargeable lithium-metal cell comprised of a current collector at the anode, a lithium film or foil as the anode, a porous separator/electrolyte layer, a cathode active material (e.g., a lithium-free V) ₂ O ₅ And MnO ₂ ) And a current collector. Either or both of the anode current collector and the cathode current collector may be the HA-based current collector of the present invention (i.e., a highly oriented thin film derived from HA or an HA/graphene mixture).

Another example of the invention is a lithium ion capacitor (or hybrid supercapacitor) comprised of a current collector at the anode, a graphite or lithium titanate anode, a porous separator soaked with a liquid or gel electrolyte, a cathode containing a cathode active material (e.g., activated carbon with a high specific surface area), and a current collector. Again, either or both of the anode and cathode current collectors may be the HA-based current collector of the present invention.

Yet another example of the invention is another lithium ion capacitor or hybrid supercapacitor comprised of a current collector at the anode, a graphite anode (and a lithium foil sheet as part of the anode), a porous separator impregnated with a liquid electrolyte, a cathode containing a cathode active material (e.g., activated carbon with a high specific surface area), and a current collector. Again, either or both of the anode and cathode current collectors may be the HA-based current collector of the present invention.

Yet another example of the invention is a lithium-graphene cell comprised of a current collector at the anode, a porous nanostructured anode (e.g., comprising graphene sheets with high surface area on which lithium ions returning during cell recharging can deposit, the graphene sheets being mixed with surface-stabilized lithium powder particles; or having lithium foil sheets attached to the nanostructures), a porous separator soaked with a liquid electrolyte, a cathode comprising a graphene-based cathode active material (e.g., graphene oxide, or graphene fluoride sheets with high specific surface area to capture lithium ions during cell discharge), and a cathode. Again, either or both of the anode and cathode current collectors may be the HA-based current collector of the present invention.

Example 1: humic acid and reduced humic acid from leonardite

Humic acid can be extracted from weathered lignite in very high yield (in the range of 75%) by dispersing weathered lignite in an alkaline aqueous solution (pH 10). Subsequently acidifying the solution results in precipitation of humic acid powder. In the experiment, 300ml of a solution containing 1M KOH (or NH) was used with magnetic stirring ₄ OH) solution dissolved 3g of leonardite. The pH was adjusted to 10. The solution is then filtered to remove any large particles or any residual impurities.

The resulting humic acid dispersion (containing HA alone or HA with graphene oxide sheets present therein) (GO was prepared in example 3 described below) was coated onto the Cu or Ti foil surface, forming a series of Cu or Ti foil films that bound HA for subsequent heat treatment to obtain a type a current collector.

For comparison, a similar film was cast onto a glass surface and then peeled off prior to subsequent heat treatment to prepare a type B current collector.

Example 2: preparation of humic acid from coal and metal foil current collector combined with HA

In a typical procedure, 300mg of coal was suspended in concentrated sulfuric acid (60 ml) and nitric acid (20 ml) and then sonicated in a cup for 2h. The reaction was then stirred and heated in an oil bath at 100 ℃ or 120 ℃ for 24h. The solution was cooled to room temperature and poured into a beaker containing 100ml of ice, followed by the step of adding NaOH (3M) until the pH reached 7.

In one experiment, the neutral mixture was then filtered through a 0.45-mm teflon membrane and the filtrate was dialyzed in a1,000da dialysis bag for 5 days. For larger humic acid pieces, the use of cross-flow ultrafiltration can reduce the time to 1 to 2 hours. After purification, the solution was concentrated using rotary evaporation to obtain solid humic acid pieces. These individual humic acid sheets and their mixtures with graphene sheets were redispersed in solvents (ethylene glycol and alcohol, respectively) to obtain several dispersion samples for subsequent casting or coating onto Al and stainless steel foils. Both type a and type B current collectors were prepared.

Example 3: preparation of Graphene Oxide (GO) sheets from natural graphite powder

Natural graphite from esbri carbon (Ashbury Carbons) was used as the starting material. GO is obtained by following the well-known modified Hummers method, which involves two oxidation stages. In a typical procedure, the first oxidation is effected under the following conditions: 1100mg of graphite was placed in a 1000mL long-necked flask. Then, 20g of K was added to the flask ₂ S ₂ O ₈ 20g of P ₂ O ₅ And 400mL of concentrated H ₂ SO ₄ Aqueous solution (96%). The mixture was heated at reflux for 6 hours and then left undisturbed at room temperature for 20 hours. Filtering the graphite oxide and washing with distilled water until pH is reached>4.0. The wet cake-like material is recovered at the end of the first oxidation.

For the second oxidation process, the previously collected wet cake was placed in a tank containing 69mL of concentrated H ₂ SO ₄ Aqueous solution (96%) in a long-necked flask. The flask was kept in an ice bath while slowly adding 9g KMnO ₄ . Care is taken to avoid overheating. The resulting mixture was stirred at 35 ℃ for 2 hours (the color of the sample turned dark green), then 140mL of water was added. After 15 minutes, by adding 420mL of water and 15mL of 30wt% ₂ O ₂ To stop the reaction. The color of the sample turned bright yellow at this stage. To remove the metal ions, the mixture was filtered and washed with 1. The collected material was gently centrifuged at 2700g and rinsed with deionized water. The final product was a wet cake containing 1.4wt% GO (estimated from dry extract). Subsequently, a liquid dispersion of GO platelets was obtained by mild sonication of the wet-cake material diluted in deionized water.

On a separate basis, aqueous suspensions containing mixtures of GO and humic acid at different GO ratios (1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 99%) were prepared and slot die coated to produce films of various compositions.

Example 4: preparation of oriented film containing mixture of humic acid and pristine graphene sheets (0% oxygen)

In a typical procedure, 5 grams of graphite flakes milled to a size of about 20 μm or less are dispersed in 1,000ml of deionized water (containing 0.1% by weight dispersant, from DuPont) containing

FSO) to obtain a suspension. An ultrasonic energy level of 85W (Branson S450 ultrasonicator) was used for puffing, separation and size reduction of graphene sheets for a period of 15 minutes to 2 hours. The resulting graphene sheets are pristine graphene that has never been oxidized and is oxygen-free and relatively defect-free. The pristine graphene is substantially free of any non-carbon elements.

The suspension after sonication contains pristine graphene sheets dispersed in water and a surfactant dissolved therein. Humic acid was then added to the suspension and the resulting mixture suspension was further sonicated for 10 minutes to promote uniform dispersion and mixing. The dispersion was then coated onto Cu and Ti foils prior to heat treatment and, for comparison, onto glass and PET films.

Example 5: preparation of highly oriented graphite films from mixtures of fluorinated graphene sheets and humic acids

We have used several methods to produce GF, but only one method is described here as an example. In a typical procedure, highly Expanded Graphite (HEG) is prepared from an intercalation compound C ₂ F·xClF ₃ And (4) preparation. HEG was further fluorinated with chlorine trifluoride vapor to produce Fluorinated Highly Expanded Graphite (FHEG). In advanceThe cooled Teflon reactor is filled with 20-30mL of liquid pre-cooled ClF ₃ The reactor was closed and cooled to liquid nitrogen temperature. Then, no more than 1g of HEG was placed in a container with a container for ClF ₃ The gas enters the reactor and is located in an aperture within the reactor. Formed within 7 days with approximate formula C ₂ F as a grey beige product.

Subsequently, a small amount of FHEG (about 0.5 mg) was mixed with 20-30mL of organic solvent (methanol and ethanol, respectively) and subjected to sonication (280W) for 30 minutes, resulting in the formation of a homogeneous yellowish dispersion. Humic acid was then added to these dispersions at various HA to GF ratios. The dispersion was then made into a Cu foil supported film using comma coating (comma coating). The highly oriented HA film was then heat treated to varying degrees to obtain a highly conductive graphite film.

Example 6: preparation of HOHA film containing graphene nitride sheets and humic acid

Graphene Oxide (GO) synthesized in example 3 was finely ground with urea in different proportions and the granulated mixture was heated in a microwave reactor (900W) for 30s. The product was washed several times with deionized water and dried in vacuo. In this method, graphene oxide is simultaneously reduced and doped with nitrogen. The products were obtained with graphene/urea mass ratios of 1.5, 1, and 1. These graphene nitride sheets remain dispersible in water. Various amounts of HA having an oxygen content of 20.5% to 45% were added to the suspension.

The resulting nitrided graphene-HA dispersion suspension is then coated on a plastic film substrate to form a wet film, which is then dried and peeled off from the plastic film and subjected to heat treatment at different heat treatment temperatures from 80 ℃ to 2,900 ℃ to obtain a Highly Oriented Humic Acid (HOHA) film (if final HTT <1,500 ℃) or a highly ordered and conductive graphite film (if at 1,500 ℃ or higher). These films were then bonded to Ti and Cu surfaces using a resin adhesive to prepare a type B current collector. In addition, for comparative purposes, a quantity of the nitrided graphene-HA dispersion suspension was also applied to the Ti and Cu foil surfaces to form wet films, which were then dried and heat treated up to 1,500 ℃ and 1,250 ℃, respectively.

Example 7: preparation of nematic liquid crystals from humic acid flakes and highly conductive films produced from humic acid flakes

Aqueous dispersions of humic acid were prepared by dispersing the HA flakes in deionized water by mild sonication. Any acidic or ionic impurities in the dispersion are removed by dialysis, a step which is crucial for the formation of liquid crystals.

The low concentration dispersion (typically 0.05wt.% to 0.6 wt.%) that is immobilized for a sufficiently long time (usually over 2 weeks) is macroscopically phase separated into two phases. While the low density top phase is optically isotropic, the high density bottom phase exhibits outstanding optical birefringence between the two crossed polarizers. A typical nematic schlieren texture consisting of dark and light brushes was observed in the bottom phase. This is a biphasic behaviour in which an isotropic phase and a nematic phase coexist. Due to the large polydispersity of the HA molecule, the composition range of the biphasic is rather broad. It can be noted that the ionic strength and pH significantly affect the stability of the HA liquid crystal. Electrostatic repulsion of surface functional groups such as carboxylates from dissociation plays a crucial role in the stability of HA liquid crystals. Thus, reducing the repulsive interactions by increasing the ionic strength or lowering the pH increases the coagulation of the HA sheet.

We observed that when HA flakes were present at a weight fraction of 1.1%, substantially all of the HA flakes formed a liquid crystal phase, and the liquid crystal could be maintained by gradually increasing the concentration of HA to a range from 6% to 16%. The prepared humic acid dispersion exhibited a non-uniform chocolate milky appearance to the naked eye. This milky appearance may be mistaken for an aggregation or precipitation of graphene oxide, but in practice it is a nematic liquid crystal.

We obtained a thin film of dry HA by dispensing and coating the HA suspension on a polyethylene terephthalate (PET) film in a slurry coater and removing the liquid medium from the coated film. The dried film was peeled from the PET film to become a free-standing film before the heat treatment. In addition, the HA suspension was also coated on a Cu foil or Ti surface and then dried. Each film (both the free-standing film peeled from the PET and the Ti or Cu supported film) is then subjected to a different heat treatment, which typically includes a chemical joining and thermal reduction treatment at a first temperature of 80 ℃ to 300 ℃ for 1-10 hours, and at a second temperature of 1,500 ℃ to 2,850 ℃ for 0.5-5 hours. The Cu-supported film and the Ti-supported film were heat treated up to only 1,250 ℃ and 1,500 ℃, respectively. With these heat treatments, the HOHA film was also converted into a highly conductive graphite film (HOGF) under compressive stress.

Several dried HA layers (HOHA films) and the internal structure (crystal structure and orientation) of HOGF were investigated in different stages of the heat treatment. An X-ray diffraction curve of the dried HOHA layer before heat treatment, the HOHA film heat-treated at 150 ℃ for 5 hours, and the obtained HOGF was obtained. The peak at about 2 θ =12 ° of the dried HOHA layer corresponds to an inter-graphene spacing (d) of about 0.75nm ₀₀₂ ). With some heat treatment at 150 ℃, the dried film exhibited the formation of a hump centered at 22 °, indicating that the process of decreasing the interplanar spacing had begun, indicating the beginning of the chemical ligation and ordering process. D of the film (not bonded to the metal foil) by a heat treatment temperature of 2,500 ℃ for 1 hour ₀₀₂ The spacing has been reduced to about 0.336, which is close to 0.3354nm for graphite single crystals.

D of film not bonded to metal surface by heat treatment temperature of 2,750 ℃ for 1 hour ₀₀₂ The spacing has been reduced to about 0.3354nm, as with graphite single crystals. Further, a second diffraction peak having high intensity appears at 2 θ =55 ° corresponding to X-ray diffraction from the (004) plane. The intensity of the (004) peak relative to the intensity of (002), or the I (004)/I (002) ratio, on the same diffraction curve is a good indication of the degree of crystal integrity and preferred orientation of the graphene planes. It is well known in the art that for all conventional graphite materials that have been heat treated at temperatures below 2,800 ℃, the (004) peak is absent or relatively weak, with the I (004)/I (002) ratio<0.1. Graphite materials heat treated at 3,000 ℃ to 3,250 ℃ (e.g., highly oriented pyrolytic graphite, HOPG) have an I (004)/I (002) ratio in the range of 0.2 to 0.5. In contrast, 2,750 ℃ CThe HOGF prepared from the HA liquid crystal-based film for one hour exhibited an I (004)/I (002) ratio of 0.77 and a mosaic spread value of 0.21, indicating a practically perfect graphene single crystal with an exceptionally high degree of preferred orientation.

The "mosaic spread" value is obtained from the full width at half maximum of the (002) reflection in the X-ray diffraction intensity curve. This index of order characterizes the graphite or graphene crystal size (or grain size), the amount of grain boundaries and other defects, and the preferred degree of grain orientation. An almost perfect single crystal of graphite is characterized by a mosaic expansivity value of 0.2-0.4. Most of our HA-derived HOGF had a mosaic spread value in this 0.2-0.4 range when produced using a final heat treatment temperature of not less than 2,500 ℃.

It can be noted that the I (004)/I (002) ratios of all tens of flexible graphite foil compacts studied were all < <0.05, and in most cases were virtually non-existent. All graphene paper/film samples prepared with the vacuum assisted filtration method had an I (004)/I (002) ratio of <0.1 even after heat treatment at 3,000 ℃ for 2 hours. These observations further confirm the following: the HOHA films of the present invention are a new and unique class of materials that are fundamentally different from any paper/film/thin film of Pyrolytic Graphite (PG), flexible Graphite (FG), and conventional graphene/GO/RGO sheets/platelets (NGP).

The values of the inter-graphene spacing for the two HA liquid crystal suspension derived HOGF samples obtained by heat treatment at different temperatures over a wide temperature range are summarized in fig. 5 (a). The corresponding oxygen content values are shown in fig. 5 (B). To show the correlation between the inter-graphene spacing and the oxygen content, the data in fig. 5 (a) and 5 (B) are re-plotted in fig. 5 (C). Careful observation of fig. 5 (a) to 5 (C) shows that there are four HTT ranges (100 ℃ -300 ℃;300 ℃ -1,500 ℃;1,500 ℃ -2,000 ℃; and >2,000 ℃), which yield four corresponding ranges of oxygen content and inter-graphene spacing. The thermal conductivity (also plotted as a function of the same final heat treatment temperature range) of the HA liquid crystal derived HOGF samples and the corresponding Flexible Graphite (FG) foil samples are summarized in fig. 5 (D). All these samples have comparable thickness values.

It is important to note that heat treatment temperatures as low as 500 c are sufficient to bring the average interplanar spacing below 0.4nm and closer to the average interplanar spacing of natural graphite or graphite single crystals. The wonderful point of the method lies in the following points: this HA liquid crystal suspension strategy enables us to recombine, reorient and chemically merge planar HA sheets into a unified structure, where all graphene-like planes are now large in lateral dimension (significantly larger than the length and width of the hexagonal carbon planes in the original HA molecule) and substantially parallel to each other. This HAs resulted in thermal conductivities that are already 300-400W/mK (HTT 500 ℃) and >623W/mK (from HA alone) or >900W/mK (from a mixture of HA + GO) (HTT 700 ℃), which is more than 3 to 4 times greater than the value of the corresponding flexible graphite foil (200W/mK). Furthermore, the tensile strength of the HOGF sample reached 90-125MPa (fig. 7 (a)).

The resulting highly oriented HA film exhibited thermal conductivities of 756W/mK (from HA alone) and 1,105w/mK (from the HA-GO mixture), respectively, with HTTs as low as 1,000 ℃. This is in sharp contrast to 268W/mK for the flexible graphite foil observed with the same heat treatment temperature. In fact, the flexible graphite foil only shows thermal conductivities below 600W/mK, no matter how high the HTT is (e.g. even up to 2,800 ℃). The HOGF layers of the present invention provided a thermal conductivity of 1,745w/mK for the layer derived from the mixture of HA and GO at an HTT of 2,800 ℃ (fig. 4 (a) and fig. 5 (D)). It may be further noted that, as shown in fig. 4 (a), the values of thermal conductivity of the HA/GO mixture-derived graphite film are consistently higher than those of the corresponding graphite film derived from graphene oxide. This unexpected effect is further discussed in example 8.

Scanning Electron Microscope (SEM), transmission Electron Microscope (TEM) images of the crystal lattice of the graphene layer, and selected area electron diffraction (SAD), bright Field (BF), and Dark Field (DF) images were also performed to characterize the structure of the monolithic graphene material. To measure the cross-sectional view of the film, the sample was buried in a polymer matrix, sectioned using a microtome, and etched with an Ar plasma.

Careful study and comparison of fig. 2, 3 (a) and 3 (B) shows that similar graphene layers in HOGF are oriented substantially parallel to each other; this is not the case for flexible graphite foils and graphene oxide papers. The tilt angle between two identifiable layers in a highly conductive graphite film is typically less than 10 degrees and in most cases less than 5 degrees. In contrast, there are so many folded graphite flakes, kinks and misorientations in the flexible graphite that many of the angles between two graphite flakes are greater than 10 degrees, some up to 45 degrees (fig. 2). Although not as poor, the misorientation between graphene platelets in NGP paper (fig. 3 (B)) is also high and there are many gaps between the platelets. The HOGF entity is substantially gapless.

Fig. 4 (a) shows the thermal conductivity values of HA/GO derived films, HA suspension derived HOGF, and Flexible Graphite (FG) foil, respectively, all plotted as a function of final HTT. These data have clearly demonstrated the superiority of the HA/GO derived HOGF structures of the present invention in terms of achievable thermal conductivity at a given heat treatment temperature.

1) HA/GO liquid crystal suspension derived HOGF appeared to be superior to GO gel derived HOGF in thermal conductivity at comparable final heat treatment temperatures. Even after thermal reduction and re-graphitization, severe oxidation of graphene sheets in GO gels can lead to high defect numbers on the graphene surface. However, the presence of HA molecules appears to be able to help repair defects or bridge gaps between GO sheets.

2) While highly oriented films derived from HA alone exhibit thermal conductivity values slightly lower than those derived from GO alone, HA as a material is abundant in nature and it does not require the use of undesirable chemicals to produce HA. HA is an order of magnitude cheaper than natural graphite (the feedstock for GO) and 2-4 orders of magnitude cheaper than GO.

3) For comparison, we also obtained a conventional Highly Oriented Pyrolytic Graphite (HOPG) sample from the Polyimide (PI) carbonization route. The polyimide film was carbonized at 500 ℃ for 1 hour, at 1,000 ℃ for 3 hours, and at 1,500 ℃ for 12 hours in an inert atmosphere. The carbonized PI film is then graphitized under a compressive force at a temperature in the range of 2,500 ℃ to 3,000 ℃ for 1 to 5 hours to form the conventional HOPG structure.

Fig. 4 (B) shows the thermal conductivity values for HA/GO suspension derived HOGF, HA suspension derived HOGF, and polyimide derived HOPG, all plotted as a function of final heat treatment temperature. These data show that conventional HOPG produced by using the carbonized Polyimide (PI) pathway exhibits consistently lower thermal conductivity compared to HA/GO derived hopfs, assuming the same HTT for the same length of heat treatment time. For example, HOPG from PI exhibits a thermal conductivity of 820W/mK after graphitization treatment at 2,000 ℃ for 1 hour. The HA/GO-derived HOGF exhibits thermal conductivity values of 1,586W/mK at the same final graphitization temperature. It can be noted that PI is also orders of magnitude more expensive than HA, and that the production of PI involves the use of several environmentally undesirable organic solvents.

4) These observations have demonstrated a clear and significant advantage of using HA/GO or HA suspension processes to produce HOGF over conventional PG processes to produce oriented graphite crystals. In fact, the thermal conductivity is always lower than that of HA/GO liquid crystal derived HOGF, no matter how long the HOPG graphitization time is. It has also been unexpectedly found that humic acid molecules can be chemically linked to each other to form strong and highly conductive graphite membranes. It is clear that highly oriented HA films (including highly oriented HA/GO films) and subsequent heat treatment profiles are fundamentally different and clearly distinct from Flexible Graphite (FG) foils, graphene/GO/RGO papers/films, and Pyrolytic Graphite (PG) in terms of chemical composition, crystal and defect structure, crystal orientation, morphology, production process and properties.

5) The data in fig. 4 (C) further supports the above conclusions, showing that the HA/GO suspension-derived HOGF and HA suspension-derived HOGF conductivity values are much better than those of FG foils over the entire range of the final HTT studied.

Example 8: effect of graphene addition on the properties of HA-based highly oriented graphite films and graphite films derived therefrom

Various amounts of Graphene Oxide (GO) sheets were added to the HA suspension to obtain a mixture suspension, wherein the HA and GO sheets were dispersed in a liquid medium. Samples of HOGF at various GO ratios were then produced following the same procedure as described above. The thermal conductivity data for these samples is summarized in fig. 6, indicating that the thermal conductivity values for HOGF produced from the HA-GO mixture are higher than those for HOGF films produced from the individual components alone.

Further unexpectedly, when both HA and GO sheets coexist in the right ratio, a synergistic effect can be observed. It appears that HA can help repair GO sheets (known to be highly defective) from their otherwise defective structure. It is also possible that HA molecules significantly smaller in size than GO sheets/molecules can fill and react with the gaps between GO molecules to bridge the gaps. Both of these factors may result in a significant improvement in conductivity.

Example 9: tensile strength of various graphene oxide-derived HOHA films

A series of HA/GO dispersion derived HOGF, GO dispersion derived HOGF and HA derived HOGF membranes were prepared by using comparable final heat treatment temperatures for all materials. Tensile properties of these materials were determined using a universal tester. Fig. 7 (a) and 7 (B) show the tensile strength and tensile modulus, respectively, of these various samples prepared in the heat treatment temperature range. For comparison, some tensile strength data for RGO paper and flexible graphite foil are also summarized in fig. 7 (a).

These data have demonstrated that the tensile strength of graphite foil derivative sheets increases slightly (from 14 to 29 MPa) with the final heat treatment temperature, and that the tensile strength of GO paper (compressed/heated sheet of GO paper) increases from 23MPa to 52MPa when the final heat treatment temperature is increased from 700 ℃ to 2,800 ℃. In contrast, the tensile strength of HA-derived HOGF increased significantly from 28MPa to 93MPa over the same heat treatment temperature range. Most notably, the tensile strength of HA/GO suspension-derived HOGF increased significantly from 32Mpa to 126Mpa. This result is quite surprising and further reflects the following view: HA/GO and HA dispersions contain highly oriented/aligned chemically active HA/GO and HA sheets/molecules that can chemically link and merge with each other during heat treatment, whereas graphene platelets in conventional GO paper and graphite flakes in FG foil are essentially dead platelets. Highly oriented films based on HA or HA/GO and subsequently produced graphitic films are themselves a new class of materials.

For reference, the film obtained by simply spraying the HA-solvent solution onto the glass surface and drying the solvent does not have any strength (it is so fragile that you can break the film simply by touching it with a finger). After heat treatment at temperatures >100 ℃, the film becomes fragmented (broken into a large number of pieces). In contrast, highly oriented HA films (where all HA molecules or sheets are highly oriented and stacked together) become films with good structural integrity with tensile strength >24MPa after heat treatment at 150 ℃ for 1 hour.

Example 10: novel effect of metal foil on thermally induced chemical ligation of humic acid molecules

Shown in fig. 8 are the thermal conductivity values for three HA-derived, highly oriented films. The first is obtained by heat-treating the HA film peeled from the glass surface. The second is coated on the Ti surface and the film is bonded to the Ti surface during the heat treatment. The third is coated on the Cu foil surface and bonded to the Cu foil surface during the heat treatment. At the same final heat treatment temperature, the metal foil supported HA films exhibited significantly higher thermal conductivity values than those of the films peeled from the PET film surface prior to heat treatment. Cu and Ti foils appear to be able to provide some catalytic effect on the thermally induced chemical linking or merging between humic acid molecules in intimate contact with Cu or Ti. This is surprising. Even more surprising is the discovery that the difference in conductivity is very large. Further, the HA membrane after heat treatment at 1,250 ℃ exhibited a thermal conductivity of 1,432w/mK when supported on a Cu foil. The HA-derived films achieved the same values after heat treatment at 2,500 ℃ for the same length of time, without the benefit of being catalyzed by Cu or Ti.

Example 11: li-S cell containing a metal foil current collector at the anode and cathode in combination with humic acid

Three (3) Li-S cells were prepared and tested, each having lithium foil as the anode active material, a sulfur/expanded graphite composite (75/25 weight ratio) as the cathode active material, 1M LiN (CF) in DOL ₃ SO ₂ ) ₂ As an electrolyte, and Celgard 2400 as a separator. First, aSeed cells (baseline cells for comparison) contained 10 μm thick Cu foil as the anode current collector and 20 μm thick Al foil as the cathode current collector. The second cell (another baseline cell for comparison) had a 10 μm thick GO-resin layer as the anode current collector and 14 μm RGO coated Al foil as the cathode current collector. The third cell had an HA-bonded Cu foil of the invention (12 μm thick total) as the anode current collector and a 20 μm thick HA-coated Al foil as the cathode current collector.

The charge storage capacity was measured periodically and recorded as a function of cycle number. The specific discharge capacity referred to herein is the total charge per unit mass of the composite cathode inserted into the cathode during discharge (the weight of the cathode active material, conductive additive or support, and binder are calculated, but the current collector is excluded). The specific energy and specific power values presented in this section are based on total cell weight (including anode and cathode, separator and electrolyte, current collector, and packaging material). Both Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to observe the morphological or microstructural changes of the selected samples after the desired number of repeated charging and recharging cycles.

Fig. 9 (a) shows the discharge capacity values of the three cells, each as a function of the number of charge/discharge cycles. For ease of comparison, each cell was designed to have an initial cell capacity of 100 mAh. It is clear that the Li-S cells characterized by the inventive HA-binding current collectors at both the anode and cathode exhibit the most stable cycling behavior, experiencing a 6% capacity loss after 50 cycles. Cells containing GO/resin coated Cu and GO coated Al current collectors suffered 23% capacity fade after 50 cycles. Cells containing Cu foil anode current collectors and Al foil cathode current collectors suffered 26% capacity fade after 50 cycles. Post-cycle inspection of these cells showed that the Al foil in all prior art electrodes suffered from severe corrosion problems. In contrast, the Al current collector of the invention, which incorporates humic acid oxide, remains intact.

Fig. 9 (B) shows a Ragone plot (gravimetric power density versus gravimetric energy density) for the three cells. It is interesting to note that our HA-bonded metal foil current collectors surprisingly impart both higher energy density and higher power density to Li-S cells compared to prior art graphene/resin coated current collectors at the anode (where at the cathode is GO coated Al foil), and Cu/Al current collectors. This is quite unexpected considering that Cu foils have conductivities more than an order of magnitude higher than those of graphene and HA films.

Example 12: magnesium ion cell with HA-enabled current collectors at the anode and cathode

For preparing cathode active material (magnesium manganese silicate, mg) _1.03 Mn _0.97 SiO ₄ ) Reagent grade KCl (melting point =780 ℃) was used as a flux after drying at 150 ℃ for 3h in vacuo. Starting materials are magnesium oxide (MgO), manganese (II) carbonate (MnCO) ₃ ) And silicon dioxide (SiO) ₂ 15-20 nm) powder. The stoichiometric amount of the precursor compounds was controlled with a Mg: mn: si molar ratio of 1.03. The mixture (flux/reactant molar ratio = 4) was ground manually in a mortar by a pestle for 10 minutes and then poured into a corundum crucible. The powder mixture was then dried in vacuo at 120 ℃ for 5h to minimize the water content in the mixture. Subsequently, the mixture was immediately transferred to a tube furnace and heated at 350 ℃ for 2h in a reducing atmosphere (Ar +5wt% H2) to remove carbonate groups. After this, final firing was carried out at various temperatures for 6h at a rate of 2 ℃/min, and then naturally cooled to room temperature. Finally, the product (magnesium manganese silicate, mg) _1.03 Mn _0.97 SiO ₄ ) Washed three times with deionized water to dissolve any remaining salts, separated by centrifugation, and dried in vacuo at 100 ℃ for 2h.

The electrode (anode or cathode) is typically prepared by: 85wt% of an electrode active material (e.g., mg) _1.03 Mn _0.97 SiO ₄ Pellets, 7wt% acetylene black (Super-P), and 8wt% polyvinylidene fluoride binder (PVDF, 5wt% solids content, dissolved in N-methyl-2-pyrrolidone (NMP)) were mixed to form a slurry mixture. After coating the slurry on the intended current collector, the resulting electrode was dried in vacuum at 120 ℃ for 2h to remove the solvent before pressing. Have studied to have different setsThree cells of fluid: the first cell HAs a Cu foil bonded to HA and an Al foil bonded to HA as anode and cathode current collectors, respectively; the second cell (prior art cell) had GO/resin coated Cu foil and GO coated Al foil (without pre-etching) as anode and cathode current collectors, respectively; the third cell (prior art cell) had a Cu foil anode current collector and an Al foil cathode current collector.

Subsequently, the electrode was cut into disks (diameter =12 mm) and used as a cathode. A thin sheet of magnesium foil is attached to the anode current collector surface and a piece of porous separator (e.g., celgard 2400 membrane) is in turn stacked on top of the magnesium foil. A piece of cathode disk coated on a cathode current collector was used as a cathode and stacked on a separator layer to form a CR2032 button cell. The electrolyte used was 1M Mg (AlCl) in THF ₂ EtBu) ₂ . The cell assembly was carried out in an argon-filled glove box. CV measurements were performed using the CHI-6 electrochemical workstation at a scan rate of 1 mV/s. The electrochemical performance of the cells was also evaluated using an Arbin and/or lap electrochemical workstation by constant current charge/discharge cycling at current densities from 50mA/g to 10A/g (up to 100A/g for some cells).

Fig. 10 shows cell specific discharge capacity values of the three cells, each as a function of the number of charge/discharge cycles. It is clear that the Mg ion cell, characterized by the current collector of the invention at both the anode and the cathode, exhibits the most stable cycling behavior, experiencing a capacity loss of 2.5% after 25 cycles. Cells containing GO/resin coated Cu foil and GO coated Al foil current collectors suffered 17% capacity fade after 25 cycles. Cells containing Cu foil anode current collectors and Al foil cathode current collectors suffered a 30% capacity fade after 25 cycles. Post-cycle inspection of the cells indicated that GO/resin coated Cu foil and GO coated Al foil current collectors became swollen and showed some delamination with the cathode layer, and the Al foil suffered from severe corrosion problems. In contrast, the HA-bound metal foil current collector of the present invention remains intact.

Example 13: chemical and mechanical compatibility testing of different current collectors for different intended batteries or supercapacitors

As demonstrated in examples 11 and 12 above, the long term stability of the current collector of a battery or supercapacitor with respect to the electrolyte is a major concern. To understand the chemical stability of the different current collectors, the main work was carried out: the current collector is exposed to several representative electrolytes. After an extended period of time (e.g., 30 days), the current collector is removed from the electrolyte solution and observed using an optical and Scanning Electron Microscope (SEM). The results are summarized in table 3 below and consistently indicate that the HA-bonded metal foil current collectors of the present invention are highly compatible with all kinds of liquid electrolytes commonly used in batteries and supercapacitors. The material of the present invention is resistant to any chemical attack. These HA-protected current collectors are substantially electrochemically inert in the voltage range of 0-5.5 volts relative to Li/Li +, suitable for use with virtually any battery/capacitor electrolyte.

It may be noted that each current collector must be attached to a tab, which in turn is attached to an external circuit wire. The current collector must be mechanically compatible with the tabs and easily or easily secured or bonded thereto. We have found that CVD graphene films simply cannot be mechanically secured to the tabs without being susceptible to breakage or breakage. Even with the aid of an adhesive, the CVD film is susceptible to breakage during the procedure of attachment to the tab or battery cell packaging.

Table 3: current collector-electrolyte compatibility test results.

In summary, we have successfully developed an absolutely new, novel, unexpected, and distinctly different class of highly conductive materials: a humic acid derived film bonded to the surface of one or more metal foils. The chemical composition, structure (crystal integrity, grain size, defect number, etc.), crystal orientation, morphology, production process and properties of such new materials are fundamentally different and clearly distinct from flexible graphite foils, polymer-derived pyrolytic graphite, CVD-derived PGs (including HOPG), and catalytic CVD graphene thin films, either free-standing or coated on metal foils. The thermal conductivity, electrical conductivity, scratch resistance, surface hardness, and tensile strength exhibited by the materials of the present invention are much higher than possible with prior art flexible graphite sheets, papers of discrete graphene/GO/RGO platelets, or other graphite films. These HA-derived film structures have the best combination of excellent electrical conductivity, thermal conductivity, mechanical strength, surface scratch resistance, hardness, and no tendency to flake.

Claims (44)

1. A humic acid bonded metal foil current collector for a battery or supercapacitor, the current collector comprising:

(a) A thin metal foil having a thickness of from 1 to 30 μm and two opposing but substantially parallel major surfaces; and

(b) At least one thin film of humic acid or a mixture of humic acid and graphene sheets, wherein the thin film of humic acid or humic acid/graphene mixture is chemically bonded to at least one of the two opposing major surfaces of the metal foil;

wherein the thin film of humic acid or humic acid/graphene mixture has a thickness of from 5nm to 10 μm, an oxygen content of from 0.01 to 10% by weight, from 1.3 to 2.2g/cm when measured alone without the thin metal foil ³ A hexagonal carbon plane oriented substantially parallel to each other and to the major surface, an interplane spacing between hexagonal carbon planes of 0.335 to 0.50nm, a thermal conductivity greater than 250W/mK, and an electrical conductivity greater than 800S/cm.

2. A current collector as in claim 1, wherein each of the two opposing major surfaces is chemically bonded to the thin film of humic acid or humic acid/graphene mixture.

3. A current collector as in claim 1, wherein the thin film of humic acid or humic acid/graphene is chemically bonded to at least one of the two opposing major surfaces of the metal foil without the use of a binder or adhesive.

4. A current collector as claimed in claim 1, wherein the thin film of humic acid or humic acid/graphene is bonded to at least one of the two opposing major surfaces of the metal foil using a binder or adhesive.

5. A current collector as in claim 4, wherein the binder or adhesive is a conductive material selected from an intrinsically conductive polymer, or amorphous carbon.

6. A current collector as in claim 4, wherein the binder or adhesive is a conductive material selected from pitch, or a carbonized resin.

7. The current collector of claim 1, wherein the thin metal foil has a thickness of from 4 to 12 μ ι η and the thin film of humic acid or humic acid/graphene mixture has a thickness of from 20nm to 2 μ ι η.

8. The current collector of claim 1, wherein the at least one major surface is free of a passivating metal oxide layer thereon.

9. A current collector as in claim 1, wherein the metal foil is selected from Cu, ti, ni, stainless steel, al foil, or combinations thereof.

10. A current collector as in claim 1, wherein the thin film has an oxygen content of from 1 to 5% by weight.

11. A current collector as in claim 1, wherein the thin film has an oxygen content of less than 1%, an interplanar spacing of less than 0.345nm, and an electrical conductivity of not less than 3,000s/cm.

12. A current collector as in claim 1, wherein the thin film has an oxygen content of less than 0.1%, an interplanar spacing of less than 0.337nm, and an electrical conductivity of no less than 5,000s/cm.

13. The current collector of claim 1, wherein the thin film has an oxygen content of not greater than 0.05%, an interplanar spacing of less than 0.336nm, a mosaicking spread value of not greater than 0.7, and an electrical conductivity of not less than 8,000s/cm.

14. The current collector of claim 1, wherein the thin film has an interplanar spacing of less than 0.336nm, a mosaicking spreading value of no greater than 0.4, and an electrical conductivity of greater than 10,000s/cm.

15. The current collector of claim 1, wherein the thin film exhibits an interplanar spacing of less than 0.337nm and a mosaic spread value of less than 1.0.

16. A current collector as in claim 1, wherein the thin film is obtained by: depositing a suspension of humic acid or a mixture of humic acid and graphene sheets onto the at least one major surface under the influence of orientation-controlling stress to form a layer of humic acid or a mixture of humic acid and graphene sheets, and then heat treating the layer at a heat treatment temperature of from 80 ℃ to 1,500 ℃.

17. A current collector as in claim 16, wherein the heat treatment temperature is from 80 ℃ to 500 ℃.

18. A current collector as in claim 16, wherein the heat treatment temperature is from 80 ℃ to 200 ℃.

19. A current collector as in claim 1, wherein the film comprises mutually parallel chemically bonded humic acid molecules or chemically combined humic acid and graphene planes.

20. A current collector as in claim 1, wherein the thin film is a continuous length film having a length of not less than 5cm and a width of not less than 1 cm.

21. The current collector of claim 1, wherein the thin film has greater than 1.6g/cm when measured alone ³ And/or a tensile strength of greater than 30 MPa.

22. The current collector of claim 1, wherein the thin film has greater than 1.8g/cm when measured alone ³ And/or a tensile strength of greater than 50 MPa.

23. The current collector of claim 1, wherein the thin film has greater than 2.0g/cm when measured alone ³ And/or a tensile strength of greater than 80 MPa.

24. A rechargeable lithium battery comprising the current collector of claim 1 as an anode current collector and/or a cathode current collector.

25. A rechargeable lithium battery as claimed in claim 24, wherein the rechargeable lithium battery is a lithium ion battery.

26. A rechargeable lithium battery comprising the current collector of claim 1 as an anode current collector or a cathode current collector, said lithium battery being a lithium-sulfur cell, a lithium-selenium cell, a lithium sulfur/selenium cell, a lithium-air cell, or a lithium-carbon cell.

27. A capacitor comprising the current collector of claim 1 as an anode current collector or a cathode current collector, the capacitor being a symmetric supercapacitor, an asymmetric supercapacitor cell, or a hybrid supercapacitor-battery cell.

28. A capacitor as claimed in claim 27, wherein the capacitor is a lithium ion capacitor cell.

29. A method for producing a metal foil current collector incorporating a highly oriented humic acid film for use in a battery or supercapacitor, the method comprising:

(a) Preparing a dispersion of humic acid or chemically functionalized humic acid flakes dispersed in a liquid medium, wherein the humic acid flakes contain an oxygen content higher than 5% by weight or the chemically functionalized humic acid flakes contain a non-carbon element content higher than 5% by weight;

(b) Dispensing and depositing the humic acid or chemically functionalized humic acid dispersion onto at least one major surface of a metal foil to form a wet layer of humic acid or chemically functionalized humic acid, wherein the dispensing and depositing procedure comprises subjecting the dispersion to an orientation inducing stress;

(c) Partially or completely removing the liquid medium from the wet layer of humic acid or chemically functionalized humic acid to form a layer having hexagonal carbon planes and an interplanar spacing d of 0.4nm to 1.3nm as determined by X-ray diffraction ₀₀₂ A layer of dried humic acid or chemically functionalised humic acid; and

(d) Heat treating the layer of dry humic acid or chemically functionalized humic acid at a first heat treatment temperature above 80 ℃ for a sufficient period of time to produce the metal foil current collector incorporating the highly oriented humic acid film, wherein the humic acid film contains interconnected, merged or thermally reduced sheets of humic acid or chemically functionalized humic acid substantially parallel to each other and chemically bound to and parallel to the at least one major surface, and the humic acid film has no less than 1.3g/cm ³ A thermal conductivity of at least 250W/mK, and/or an electrical conductivity of not less than 500S/cm.

30. The method of claim 29, further comprising a step of compressing the humic acid film of the combined or reduced humic acid or chemically functionalized humic acid after step (d).

31. The method of claim 29, wherein the humic acid or chemically functionalized humic acid dispersion further contains graphene sheets or molecules dispersed therein, and the ratio of humic acid to graphene or chemically functionalized humic acid to graphene is from 1/100 to 100/1 and the graphene is selected from pristine graphene, graphene oxide, reduced graphene oxide, fluorinated graphene, brominated graphene, iodinated graphene, boron doped graphene, nitrogen doped graphene, or combinations thereof.

32. The method of claim 29, wherein the humic acid or chemically functionalized humic acid pieces are in an amount sufficient to form a liquid crystal phase in the liquid medium.

33. The method of claim 29, wherein the dispersion comprises a first volume fraction of humic acid or chemically functionalized humic acid dispersed in the liquid medium, the first volume fraction exceeding a critical volume fraction (V) for liquid crystal phase formation _c ) And the dispersion is concentrated to achieve a second volume fraction of humic acid or chemically functionalized humic acid greater than the first volume fraction to improve humic acid or chemically functionalized humic acid flake orientation.

34. The method of claim 33, wherein the first integral number corresponds to a weight fraction of humic acid or chemically functionalized humic acid in the dispersion of from 0.05% to 3.0% by weight.

35. The method of claim 34, wherein, prior to step (b), the dispersion is concentrated to contain greater than 3.0% but less than 15% by weight humic acid or chemically functionalized humic acid dispersed in the liquid medium.

36. The method of claim 29, wherein the dispersion further comprises a polymer dissolved in the liquid medium or attached to the humic acid or chemically functionalized humic acid.

37. The method of claim 29, wherein the chemically functionalized humic acid contains a chemical functional group selected from the group consisting of: SO (SO) ₃ H、NH ₂ OH, R 'CHOH, CHO, CN, COCl, halogen, COSH, COOR', SR ', siR' ₃ 、Si(--OR'--) _y R' _3-y 、Si(--O--SiR' ₂ --)OR'、R"、Li、AlR' ₂ 、Hg--X、TlZ ₂ And Mg- -X; wherein y is an integer equal to or less than 3, R 'is hydrogen, alkyl, aryl, cycloalkyl, aralkyl, cycloaryl, or poly (alkylether), R' is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl, or cycloaryl, X is halogen, and Z is carboxylate or trifluoroacetate, or a combination thereof.

38. The method of claim 31, wherein the graphene sheets comprise chemically functionalized graphene comprising a chemical functional group selected from: SO (SO) ₃ H、NH ₂ OH, R 'CHOH, CHO, CN, COCl, halogen, COSH, COOR', SR ', siR' ₃ 、Si(--OR'--) _y R' _3-y 、Si(--O--SiR' ₂ --)OR'、R"、Li、AlR' ₂ 、Hg--X、TlZ ₂ And Mg- -X; wherein y is an integer equal to or less than 3, R 'is hydrogen, alkyl, aryl, cycloalkyl, aralkyl, cycloaryl, or poly (alkylether), R' is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl, or cycloaryl, X is halogen, and Z is carboxylate or trifluoroacetate, or a combination thereof.

39. The method of claim 29, wherein the liquid medium consists of water or a mixture of water and alcohol.

40. The method of claim 29, wherein the liquid medium comprises a non-aqueous solvent selected from the group consisting of: polyethylene glycol, ethylene glycol, propylene glycol, sugar alcohols, polyglycerols, glycol ethers, amine-based solvents, amide-based solvents, alkylene carbonates, organic acids, or inorganic acids.

41. The process of claim 29, which is a roll-to-roll process, wherein step (b) comprises feeding a sheet of the metal foil from a roll to a deposition zone, depositing a layer of humic acid or chemically functionalized humic acid dispersion onto at least one major surface of the metal foil to form a wet layer of the humic acid or chemically functionalized humic acid dispersion thereon, drying the humic acid or chemically functionalized humic acid dispersion to form a layer of dried humic acid or chemically functionalized humic acid deposited on the surface of the metal foil, and collecting the metal foil on a collection roll from which the layer of humic acid or chemically functionalized humic acid is deposited.

42. The method of claim 29, wherein the first heat treatment temperature comprises a temperature in a range of 100 ℃ to 1,500 ℃, and the highly oriented humic acid film has an oxygen content of less than 2.0%, an inter-planar spacing of less than 0.35nm, no less than 1.6g/cm ³ A thermal conductivity of at least 800W/mK, and/or an electrical conductivity of not less than 2,500S/cm.

43. The method of claim 29, wherein the first heat treatment temperature comprises a temperature in a range of 1,500 ℃ to 2,100 ℃, and the highly oriented humic acid film has an oxygen content of less than 1.0%, an inter-planar spacing of less than 0.345nm, a thermal conductivity of at least 1,000w/mK, and/or an electrical conductivity of not less than 5,000s/cm.

44. The method of claim 29, wherein the humic acid or chemically functionalized humic acid sheets have a maximum original length and the highly oriented humic acid film comprises humic acid or chemically functionalized humic acid sheets having a length greater than the maximum original length.

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